PRINTER AND PRINTER CONTROL METHOD BACKGROUND OF THE INVENTION 1. Field of technology The present invention relates generally to a printer and a printer control method, and relates more particularly to the internal process of a printer when returning^from an off-line status to an-on-Iine status. 2. Description of Related Art A printer system having a printer typically has the printer connected to enable communication with a host computer which generates the print data to be printed and controls printer operations. During printing, for example, the printer executes print control commands received from the host computer to print on slips or roll paper and then output the result. When the paper runs out or a paper jam occurs inside the printer, the internal status of the printer generally goes from an on-line status, which is the printer state enabling printing, to an off-line status in which the printer does not print, ff a receipt was being printed on roll paper, for example, printing the receipt is interrupted when the printer goes off-line. The printer then returns on-line when the cause of the printer going off-line is removed after the printer has gone off-line. If the supply of roll paper inside the printer is depleted, for example, the printer is able to return online after a new roll of paper is loaded into the printer. If the roll paper jams inside the printer and the printer thus cannot advance the paper, correctly reloading the paper and then asserting a reset command enables the printer to return on-line. However, if the roll paper supply runs out, a new roll is loaded into the printer, and the printer returns on-line and then resumes printing, the remaining print data, that is, the print data that was not printed before the printer went off-line, is printed to the roll paper after the printer returns on-line. This results in the receipt content that should normally be printed to a single continuous receipt being printed on two separate pieces of paper. A problem with this is that in some circumstances a receipt that is printed on two separate pieces of paper is meaningless as a receipt. As a result, the same receipt content must be sent from the host computer to the printer again for reprinting, and this wastes paper. This also drastically reduces printing efficiency considering the time and trouble involved with reprinting a receipt, and thus lowers productivity. When the roll paper is reloaded correctly because the roll paper jammed and could not be fed, and the reset command is then asserted to return the printer on-line and resume printing, a portion of the printed paper is often skewed, creased, or badly wrinkled. As a result, the receipt content must be sent from the host computer to the printer again for reprinting. This also wastes paper, drastically reduces printing efficiency, and thus lowers productivity. Furthermore, new print data received while the printer is off-line is stored in the receive buffer, but the storage capacity of the receive buffer is limited. This means that when a large amount of data such as for a bitmapped image is received, the receive buffer could become full, thus preventing receiving any more data. JP-A-H11-268384 teaches a printer which receives from the host computer a command instructing - -the printer what process