Added file extension for nvram files when ROM filename is provided

[MikePinball]

Getting high scores for Visual Pinball/VPinMAME doesn't work that well. Multiple ROM names mean nothing is chosen. One way to resolve this is to explicitly provide the ROM name in the table setup. However the ".nv" file extension is not added by the code and so the NMRAM file with the scores is still not found.

This code was tested with the TOTAN ROM that has at least two ROM files (totan_12.zip and totan_14.zip).