The present disclosure relates to a thin-film element assembly. BACKGROUND Presently, in image display devices such as display devices having an organic electroluminescent element (organic EL element) or a microcapsule-type electrophoretic display element, or a liquid crystal display device, realization of image display devices having flexibility is desired. Image display devices having flexibility have a large screen and are thin, light, and rollable, and are easy to carry. However, on the other hand, when such an image display device is rolled up, a problem such as the occurrence of scratches or abrasion resulting from friction between contact surfaces is likely to occur. In order to deal with such a problem, JP-A-2008-185853, for example, discloses a disclosure relating to a flexible display device in which light-emitting elements are formed on a flexible base, and which is rolled up for storage so that a light-emitting-side surface and a rear-side surface are in contact with each other, and in which the hardness of the light-emitting-side surface is larger than the hardness of the rear-side surface. 2 SUMMARY However, in the flexible display device disclosed in JP-A-2008-185853, a further improvement in durability is desired. Therefore, it is desirable to provide a thin-film element assembly having a configuration and structure capable of achieving a further improvement in durability. In a thin-film element assembly of an embodiment of the present disclosure, a plurality of thin-film elements are provided on a first surface of a base having flexibility, a second region where no thin-film element is provided is formed in the base in an outer side of a first region where a plurality of thin-film elements are provided, and convex portions are formed in the second region of the first surface of the base, or the second region of a second surface, or the second region of each of the first and second surfaces. In the thin-film element assembly of the embodiment of the present disclosure, since the convex portions are formed in the second region of the base where no thin-film element is provided, even when the thin-film element assembly is rolled up, it is possible to reliably prevent the second surface of the base from making contact with the plurality of thin-film elements formed on the first surface, and to provide more durability to the thin-film element assembly. 3 BRIEF DESCRIPTION OF THE DRAWINGS Fig. lA is a schematic side view of a thin-film element assembly according to a first embodiment as seen from a first direction, and Fig. 1B is a schematic perspective view of the thin-film element assembly as seen from a second surface side. Fig. 2A is a schematic perspective view of the thin-film element assembly according to the first embodiment as seen from a first surface side, and Fig. 2B is a schematic perspective view of a thin-film element assembly according to a second embodiment as seen from a second surface side. Fig. 3A is a schematic side view of a thin-film element assembly according to a third embodiment as seen from a first direction, and Fig. 3B is a schematic perspective view of the thin-film element assembly as seen from. a second surface side. Fig. 4A is a schematic side view of a thin-film element assembly according to a fourth embodiment as seen from a first direction, and Fig. 4B is a schematic perspective view of the thin-film element assembly as seen from a first surface side. Fig. 5 is a schematic perspective view of a thin-film element assembly according to a fifth embodiment as seen from a first surface side. Figs. 6A and 6B are schematic side views of thin-film element assemblies according to a sixth embodiment and a modification example thereof as seen from a first direction, 4 respectively. Figs. 7A and 7B are schematic partial cross-sectional views of thin-film elements according to seventh and eighth embodiments, respectively. Figs. 8A and 8B are schematic partial cross-sectional views of thin-film elements according to ninth and tenth embodiments, respectively. Fig. 9 is a schematic partial cross-sectional view of a thin-film element according to an eleventh embodiment. Fig. l0A is a schematic partial cross-sectional view of a modification of a thin-film element assembly of an embodiment, and Fig. lOB is a schematic partial cross-sectional view of a support substrate or the like, for explaining a method of manufacturing a thin-film element assembly according to an embodiment. DETAILED DESCRIPTION Hereinafter, the present disclosure will be described based on embodiments by referring to the drawings throughout which like parts are referred to by like references. However, the present disclosure is not limited to the embodiments, and various numerical values and materials described in the embodiments are only examples. The description will be given in the following order. 1. Overall Description of Thin-Film Element Assembly 5 according to Present Disclosure 2. First Embodiment (Thin-Film Element Assembly according to Present Disclosure) 3. Second Embodiment (Modification of First Embodiment) 4. Third Embodiment (Another Modification of First Embodiment) 5. Fourth Embodiment (Still Another Modification of First Embodiment) 6. Fifth Embodiment (Modification of Fourth Embodiment) 7. Sixth Embodiment (Modifications of First and Fourth Embodiments) 8. Seventh Embodiment (Modifications of First to Sixth Embodiments) 9. Eighth Embodiment (Another Modification of First to Sixth Embodiments) 10. Ninth Embodiment (Still Another Modification of First to Sixth Embodiments) 11. Tenth Embodiment (Still Another Modification of First to Sixth Embodiments) 12. Eleventh Embodiment (Still Another Modification of First to Sixth Embodiments) and Alternative Embodiment [Overall Description of Thin-Film Element Assembly according to Present Disclosure] In a thin-film element assembly according to the present 6 disclosure, a base may have a rectangular shape such that two opposite sides extend in a first direction, and the other two opposite sides extend in a second direction, and convex portions may be formed in a second region along the two sides extending in the first direction. In such a preferred configuration, the base is rollable about an axial line parallel to the second direction. That is, the base is rollable along the first direction. In such a preferred configuration, each of the convex portions may have a notch portion extending in parallel to the second direction. In these preferred configurations, the thin-film element assembly may have such a structure in which the convex portions are formed in the second region of a second surface of the base, or the second region of each of the first and second surfaces of the base, a reinforcing member extending in the second direction is formed in at least a first region of the second surface of the base, and the height of the reinforcing member is lower than the height of the convex portion formed in the second region of the second surface of the base. In the thin-film element assembly according to the present disclosure including these preferred configurations and structure, the thin-film element assembly may have such a structure in which: 7 the convex portions are formed in the second region of the first surface of the base or the second region of each of the first and second surfaces'of the base, and additional convex portions are formed in the second region of the first surface of the base along the second sides extending in the second direction. That is, in such a structure, the convex portions are provided in a frame shape in the second region of the first surface of the base so as to surround the first region. In the thin-film element assemblies according to the present disclosure including the above-described preferred configurations and structures, the convex portions are preferably formed of at least one material selected from a group consisting of an expanded material, a gel-like material, and a rubber-like material. In this case, it is still preferable that the convex portions contain an antistatic agent. In the thin-film element assemblies according to the present disclosure including the above-described preferred configurations and structures (hereinafter, these will be collectively referred to simply as the "thin-film element assembly according to the present disclosure), although the base has flexibility, the expression "the base has flexibility" means that the base is not broken even when it is rolled around a cylinder having a radius of 5 cm when the base has a thickness of 1 mm or smaller and around a cylinder having a radius of 8 20 cm when the base has a thickness of 1 mm or more. Moreover, although the thin-film element assembly according to the present disclosure generally has flexibility, the expression "the thin-film element assembly has flexibility" means that the thin-film element assembly is not broken even when it is rolled around a cylinder of a radius of 20 cm. In the thin-film element assembly according to the present disclosure, examples of the expanded material include urethane foam and acrylic foam, examples of the gel-like material include silicone gel and acrylic gel, and examples of the rubber-like material include silicone rubber, ethylene propylene-diene rubber (EPDM), chloroprene rubber (CR), NBR, SBR, isoprene rubber (IR) , and natural rubber, examples of the antistatic agent include carbon, titanium oxide, carbon nanotubes, copper, aluminum, surfactants, an ionic conductivity mechanism, and an electron conduction mechanism. However, the material constituting the convex portions is not limited to the above materials, but plastic material constituting the base described later may be used. In this case, the plastic material constituting the base may be the same as or different from the plastic material constituting the convex portions. The material constituting the reinforcing member may include the above materials, and alternatively, the plastic material constituting the base described later may be used. In this case, the plastic material 9 constituting the base may be the same as or different from the plastic material constituting the reinforcing member. Alternatively, examples of the material constituting the reinforcing member include polyethylene resin (PE), polyethylene terephthalate resin (PET), ethylene vinyl acetate copolymer (EVA), polyvinyl chloride resin (PVC), polypropylene resin (PP), polystyrene resin (PS), acrylonitrile-styrene-butadiene polymerized resin (ABS), cyclic olefin copolymer (COC), polycarbonate resin (PC), polyamide resin (PA), phenolic resins, and TPE. Examples of a method of manufacturing the convex portion and the reinforcing member include a method of punching a sheet-shaped member with a die, an injection molding method, and an extrusion molding method. The manufactured convex portion and the reinforcing member may be attached to the base using an adhesive, and alternatively, the manufactured convex portion and reinforcing member may be fixed to the base based on a thermal fusion bonding method, a photo-curing method, and a method using a bonding tape. Alternatively, the convex portion and the reinforcing member may be directly formed on the base. Moreover, the convex portions and the reinforcing member may be formed to be integrated with each other, and the convex portion and the reinforcing member may be formed to be integrated with the base. The convex portions may have a strip-like shape, a shape formed by a set of line segments, 10 and a shape formed by a set of dots. The number of convex portions in the second region along one side extending in the first direction may be one or plural. The convex portions formed in the second region of the first surface of the base will be referred to as "first convex portions" for convenience, and the convex portions formed in the second region of the second surface of the base will be referred to as "second convex portions" for convenience. In the thin-film element assembly according to the present disclosure, examples of the material constituting the base include at least one resin (plastic material or plastic film) selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide, polycarbonate (PC), polyether sulfone, polymethyl methacrylate (poly (methyl methacrylate), PMMA), polyvinyl alcohol (PVA), polyvinyl phenol (PVP) , polysulfone, polyether sulfone (PES), and polysulfone imide, and alternatively, thin-film glass, metal foil such as stainless steel foil or aluminum foil, and alloy foil. In the thin-film element assembly according to the present disclosure, when the height of the convex portion is H, and the distance between the two opposite sides parallel to the first direction of the base is W, the value of H is preferably sufficiently smaller than the value of W. Moreover, in the thin-film element assembly according to the present 11 disclosure, when the height of the reinforcing member is H3, and the height of the second convex portion is H2, it is preferable that a relation of H3<142 is satisfied. Moreover, when the thickness of the thin-film element is Ho, and the height of the first convex portion is H1, it is necessary to satisfy a relation of Ho