Nibble code doesn't check data epilog bytes

[fadden]

The DiskImg::NibbleDescr struct has a dataEpilogVerifyCount field, but it's never actually used. This omission allows the "standard" profile to read some disks that it shouldn't (e.g. MECC).

Not really a problem, especially since the auto-detection would just switch to the "patched" profile (which explicitly skips checking the epilogs), but the behavior tells the user that the disk has a standard format when it doesn't.