the special wallpaper values are +0x10 (ie 0x20, 0x21... instead of
0x10, 0x11) from the contiguous sequence of regular box wallpaper IDs
(anti cheat probing?).
Xor tweak allows for single invert method; use this invert with the base
implementation's method.
Range check for setting the box wallpaper (just in case). The underlying
error was fixed; the 255 val was reading from the wrong offset (now
fixed).
Thanks Scarfy!
https://projectpokemon.org/forums/files/file/1-pkhex/?do=findComment&comment=344
