The invention relates to the repair of parts made of composite material which comprise a fibrous reinforcement obtained by three-dimensional weaving densified by a matrix. Prior art Parts made of composite material comprising a reinforcement obtained by three-dimensional weaving have the advantage of having a “non-delaminable” character compared to parts made of composite material in which the fibrous reinforcement is obtained by stacking or draping two-dimensional fibrous plies. Composite material parts made from two-dimensional fibrous plies are easily repairable because the plies are separable and can therefore be replaced by new sound plies in the event of damage. Examples of repair solutions for parts made of composite material are described in particular in documents US 2015/0185128, US 2012/0080135 and US 2007/0095457. These known solutions consist in sticking a pre-impregnated fibrous patch on the damaged area or the area to be recovered from the part made of composite material, the patch possibly consisting of one or more fibrous folds. However, this type of solution presents a risk of delamination of the bonded patch and is therefore undesirable for the repair of parts made of composite material with three-dimensional fiber reinforcement because the material would then lose its “non-delaminable” character. However, there is a need for a solution for repairing parts made of composite material with three-dimensional fiber reinforcement which does not alter the resistance to delamination initially presented by the material. Disclosure of the invention To this end, the invention provides a method for repairing a part made of composite material comprising a fibrous reinforcement exhibiting a three-dimensional weaving between a plurality of warp yarns and a plurality of weft yarns, said fibrous reinforcement being densified by a matrix. , characterized in that it comprises: - identification of at least one damaged area in the room, - The production of a recessed portion by removing the composite material from the damaged area so as to form a recessed portion extending from a first face of the part made of composite material to a second face of said part, - The production of a first plurality of grooves extending over the first face of the part made of composite material from the edge (s) of the recessed portion, - The production of a second plurality of grooves extending over the second face of the part made of composite material from the edge (s) of the recessed portion, - The production of a plurality of orifices in the thickness of the part made of composite material, each orifice opening out both into a groove of the first plurality of grooves and into a groove of the second plurality of grooves, - the three-dimensional weaving of at least a fiber preform of a filling piece comprising a central portion having a shape corresponding to the shape of the recessed portion of the piece made of composite material and a plurality of fiber bundles extending from the central portion, - the placement of the central portion of the fiber part preform of filling in the free volume of the composite material part delimited by the recessed portion, - the placement of a first part of the fiber bundles of said at least one preform in the grooves of the first plurality of grooves present on the first face of the part and in the orifices of the plurality of orifices so that the fibrous bundles of the first part of fibrous bundles of said at least one preform open into the grooves of the second plurality of grooves, - the placement of a second part of the fibrous bundles of said at least one preform in the grooves of the second plurality of grooves present on the second face of the part and in the orifices of the plurality of orifices so that the fibrous bundles of the second of fibrous bundles of said at least one preform open into the grooves of the first plurality of grooves, - the impregnation of said at least one fiber preform with a resin precursor of a matrix, - The transformation of the resin into a matrix in order to obtain a filling part made of composite material comprising a fibrous reinforcement densified by a matrix, said filling part occupying the volume defined by the recessed portion. By using a filling piece comprising at least one preform having a central portion exhibiting a three-dimensional weave which mechanically attached to the piece by fiber bundles, it is possible to make repairs which exhibit high resistance to delamination. The repair of a damaged area in the part made of composite material according to the invention is therefore particularly robust. According to a first characteristic of the method of the invention, the repair method comprises: - the three-dimensional weaving of a first fiber preform of a piece of filling comprising a central portion having a shape corresponding to the shape of the recessed portion on the side of the first face of the part made of composite material and a plurality of fibrous bundles extending from the central portion, - the three-dimensional weaving of a second fiber preform of a piece of filling comprising a central portion having a shape corresponding to the shape of the recessed portion on the side of the second face of the part made of composite material and a plurality of fibrous bundles extending from the central portion, - Placement of the central portion of the first fiber preform of the filling part in a part of the free volume of the part made of composite material delimited by the recessed portion and present on the side of the first face of the part and of the fibrous bundles in the grooves of the first plurality of grooves present on the first face of the part and in the orifices of the plurality of orifices so that the fiber bundles of the first preform open into the grooves of the second plurality of grooves, - The placement of the central portion of the second fiber preform of the filling part in another part of the free volume of the part made of composite material delimited by the recessed portion and present on the side of the second face of the part and of the fibrous bundles in the grooves of the second plurality of grooves present on the second face of the part and in the orifices of the plurality of orifices so that the fibrous bundles of the second preform open into the grooves of the first plurality of grooves, According to a second characteristic of the method of the invention, the production of the hollowed-out portion comprises the formation of several facing edges each comprising first and second bevels, the central portion of the first fiber preform of the filling piece having a geometry complementary to a part of the volume of the recessed portion defined between the first bevels of the facing edges and the central portion of the second fiber preform of a filling piece having a geometry complementary to the other part of the volume of the recessed portion defined between the second bevels of the opposite edges. This makes it possible to optimize the transmission of mechanical loads on the bonding interface between the filling part and the composite material structure of the part to be repaired. According to a third characteristic of the method of the invention, the recessed portion has a polygonal shape, the grooves of the first plurality of grooves each extending from a vertex of the polygon formed by the recessed portion on the first face of the part made of composite material, the grooves of the second plurality of grooves each extending from a vertex of the polygon formed by the portion recessed on the second face of the part made of composite material. This makes it possible to obtain a balanced attachment configuration for each fiber preform of a filling piece and thus to strengthen the retention of the filling piece on the piece of composite material to be repaired. According to a fourth characteristic of the method of the invention, the first and second pluralities of grooves each comprise main grooves extending from the edges of the recessed portion opening respectively on the first and second faces of the part made of composite material and secondary grooves extending from each main groove, at least part of the orifices of the plurality of holes both opening into one groove secondary of the first plurality of grooves and in a secondary groove of the second plurality of grooves. It is thus possible to form an attachment network in the shape of a “snowflake” for each fiber preform of a piece of fabric. filling and thus strengthen the retention of the filling part on the composite material part to be repaired. According to a fifth characteristic of the method of the invention, the latter further comprises the introduction of the fiber bundles of the first fiber preform of the filling part into the central portion of the second fiber preform and the introduction of the fiber bundles of the filling part. second fiber preform of filling piece in the central portion of the first fiber preform. This makes it possible to further strengthen the retention of the fiber preforms on the part made of composite material and to improve the strength of the filling part. A subject of the invention is also a part made of composite material comprising a fibrous reinforcement having a three-dimensional weaving between a plurality of warp yarns and a plurality of weft yarns, said fibrous reinforcement being densified by a matrix, characterized in that the reinforcement fibrous fiber densified by the matrix comprises at least one recessed portion extending from a first face of the part made of composite material to a second face of said part and in that a filling part made of composite material is present in the volume free of the composite material part delimited by said at least one recessed portion,the part made of composite material comprising a first plurality of grooves extending over the first face of said part from the edge or edges of the recessed portion opening onto the first face and a second plurality of grooves extending over the second face of said part from one or more edges of the recessed portion opening onto the second face, the part made of composite material further comprising a plurality of orifices extending in the thickness of the part made of composite material, each orifice opening into the both in a groove of the first plurality of grooves and in a groove of the second plurality of grooves,the filling piece comprising at least one fiber preform of the filling piece comprising a central portion present in the volume of the recessed portion and a plurality of fiber bundles extending from the central portion, the central portion of said at least one preform having a weaving three-dimensional, a first part of the fiber bundles of said at least one fiber preform being present in the grooves of the first plurality of grooves present on the first face of the part made of composite material and in the orifices of the plurality of orifices so as to that the fibrous bundles of the first part of the fibrous bundles of said at least one preform open into the grooves of the second plurality of grooves,a second part of fiber bundles of said at least one fiber preform being present in the grooves of the second plurality of grooves present on the second face of the part made of composite material and in the orifices of the plurality of orifices so that the fibrous bundles of the second part of the fibrous bundles of said at least one preform open into the grooves of the first plurality of grooves. According to a first characteristic of the part of the invention, the part of filler comprises first and second fiber preforms of filler piece each comprising a central portion present in a part of the volume of the recessed portion and a plurality of fiber bundles extending from the central portion, the central portion of each preform having a weave three-dimensional, the fiber bundles of the first fiber preform being present in the grooves of the first plurality of grooves present on the first face of the piece of composite material and in the orifices of the plurality of orifices so that the fiber bundles of the first preform open into the grooves of the second plurality of grooves,the fiber bundles of the second fiber preform being present in the grooves of the second plurality of grooves present on the second face of the part made of composite material and in the orifices of the plurality of orifices so that the fiber bundles of the second preform open into the grooves of the first plurality of grooves. According to a second characteristic of the part of the invention, the recessed portion comprises at least two facing edges each comprising first and second bevels, the central portion of the first fiber preform of a filling part having a complementary geometry. of a part of the volume of the recessed portion defined between the first bevels of the facing edges and the central portion of the second fiber preform of a filler piece having a geometry complementary to the other part of the volume of the portion recessed defined between the second bevels of the opposite edges. According to a third characteristic of the part of the invention, the recessed portion has a polygonal shape, the grooves of the first plurality of grooves each extending from a vertex of the polygon formed by the recessed portion on the first face of the part made of composite material, the grooves of the second plurality of grooves each extending from a vertex of the polygon formed by the recessed portion on the second face of the part of composite material. According to a fourth characteristic of the part of the invention, the first and second pluralities of grooves each comprise main grooves extending from the edges of the recessed portion opening respectively on the first and second faces of the part made of composite material and secondary grooves extending from each main groove, at least part of the orifices of the plurality of holes both opening into one groove secondary of the first plurality of grooves and in a secondary groove of the second plurality of grooves. According to a fifth characteristic of the piece of the invention, the fiber bundles of the first fiber preform of the filling piece extend in the central portion of the second fiber preform and the fiber bundles of the second fiber preform of the filling piece s 'extend into the central portion of the first fiber preform. According to a sixth characteristic of the part of the invention, the part corresponds to a casing of an aeronautical gas turbine engine. In this case, the subject of the invention is also an aeronautical gas turbine engine having a casing according to the invention, for example a fan casing, as well as an aircraft comprising one or more of these aeronautical engines. Brief description of the drawings [Fig. 1] Figure 1 is a perspective view of an aircraft engine comprising a fan housing, [Fig. 2A] FIG. 2A is a top view of an impact zone on the fan housing of the engine of FIG. 1, [Fig. 2B] FIG. 2B is a radial sectional view of an impact zone on the fan housing of the engine of FIG. 1, [Fig. 3A] FIG. 3A is a top view showing the production of a recessed portion in the fan casing in accordance with one embodiment of the invention, [Fig. 3B] FIG. 3B is a radial sectional view showing the production of a recessed portion in the fan casing in accordance with one embodiment of the invention, [Fig. 4A] Fig. 4A is a top view showing one side showing the formation on both sides of the fan housing of grooves around the recessed portion, [Fig. 4B] Figure 4B is a radial sectional view showing the formation on both sides of the fan housing of grooves around the recessed portion, [Fig. 5A] FIG. 5A is a top view showing the face showing the formation of a plurality of orifices in the fan casing opening into the grooves of FIGS. 4A and 4B, [Fig. 5B] Figure 5B is a radial sectional view showing the formation of a plurality of orifices in the fan housing opening into the grooves of Figures 4A and 4B, [Fig. 6A] FIG. 6A is a top view showing the external face showing the placement of fiber preforms of a filling piece, [Fig. 6B] FIG. 6B is a bottom view showing an internal face showing the placement of fiber preforms of a filling piece, [Fig. 6C] FIG. 6C is a radial sectional view showing the placement of fiber preforms of a filling piece, [Fig. 7A] FIG. 7A is a top view showing the external face showing the placement of the fiber bundles of a fiber preform of FIG. 6A, [Fig. 7B] Figure 7B is a radial sectional view showing the placement of the fiber bundles of each fiber preform of Figures 6A and 6B, [Fig. 8A] FIG. 8A is a top view showing an external face showing the production of a filling part in the fan casing, [Fig. 8B] FIG. 8B is a view in radial section showing the production of a filling part in the fan casing, [Fig. 9] FIG. 9 is a sectional view showing a fiber preform of a filling piece according to another embodiment of the invention, [Fig. 10] Figure 10 is a radial sectional view showing the placement of the fiber bundles of the preform of Figure 9. Description of the embodiments The invention applies generally to any part made of composite material comprising a fibrous reinforcement exhibiting a three-dimensional weaving, the reinforcement being densified by a matrix. The invention will be described below in the non-limiting context of its application to a fan casing of a gas turbine aeronautical engine. The invention also applies to other composite material parts of aeronautical engines such as, for example, fixed guide vanes also called “OGV” or inter-vane platforms. Such an engine, as shown very schematically in FIG. 1, comprises, from upstream to downstream in the direction of the gas flow, a fan 1 disposed at the inlet of the engine, a compressor 2, a chamber of combustion 3, a high-pressure turbine 4 and a low-pressure turbine 5. The engine is housed inside a housing comprising several parts corresponding to different parts of the engine. Thus, the fan 1 is surrounded by a fan casing 10 having a shape of revolution. The fan casing 10 which is here made of a composite material with an organic matrix, that is to say from a reinforcement of fibers, for example of carbon, glass, aramid or ceramic, densified by a polymer matrix, by example epoxy, bismaleimide or polyimide. The fibrous reinforcement is made from a fibrous texture in the form of a strip obtained by three-dimensional weaving in a single piece, the texture being shaped by winding on a support tool. The fibrous reinforcement thus formed is then densified by a matrix. The manufacture of such a housing is described in particular in document US Pat. No. 8,322,971. blower made of composite material 10 has an internal face 11 which defines the air inlet duct of the engine and an external face 12. In Figures 1, 2A and 2B, the housing 10 has a damaged area 20 resulting for example from blade debris projected onto the inner surface 1 1 of the housing. In accordance with the repair method of the invention, the housing is machined at the damaged area 20 to remove the affected composite material and prepare the area for repair. The removal of the composite material is carried out on a determined surface of the casing covering at least the area identified as damaged and over the entire thickness of the housing. As illustrated in FIGS. 3A and 3B, a recessed portion 30 is thus obtained which opens out both on the internal face 1 1 and on the external face 12 of the casing 10. In the example described here and according to a particular characteristic of the invention, the recessed portion is machined in a polygonal shape with edges 31 to 36 each comprising two prismatic shapes or bevels of height h having a common apex. More precisely, the edges 31 to 36 each comprise respectively a first bevel like the bevels 320 and 340 illustrated in FIG. 3B respectively for the edges 32 and 34 and a second bevel like the bevels 321 and 341 illustrated in FIG. 3B respectively for the edges 32 and 34. The edges can be machined. stepped as in Figure 3B or following a smooth profile. Each angular edge has a fillet r not shown in FIG. 3B. The height h of the bevels and the fillet r are determined as a function of the diameter D of the damaged zone 20 and the thickness E of the composite material to be repaired. The height h is preferably determined such that E / 3