Bug with pctosnes in ExLoROM mapping

[trillllian]

In ExLoROM, it's possible for pctosnes to return $7E0000-$7FFFFF.

00-3F:8000-FFFF           -> x400000-x5FFFFF
40-7F:8000-FFFF (+mirror) -> x600000-x7FFFFF
80-BF:8000-FFFF           -> x000000-x1FFFFF
C0-FF:8000-FFFF (+mirror) -> x200000-x3FFFFF

I hope it's possible to understand this kinda confusing mapping description. 0x7F0000-0x7FFFFF "should" go to $7E:8000/$7F:8000 but obviously there's RAM there. This means that PC 0x7F0000-0x7FFFFF is actually completely inaccessible, meaning the practical maximum rom size is 0x7F0000. This should be accounted for in pctosnes and the freespace finder.

(marking this is priority:low because who even uses exlorom lol)