Some DOSBox Raw OPL v2 indices were off by one.

This caused access violation errors on perfectly fine DRO files. For
reference, scoredata[20] is the hardware type (OPL2, dual OPL2, or
OPL3).
The wrong value was used here.

This caused crashes on some files (notably MBELLS from Cosmo and NUBC
from Body Count) in my port of this code to SLADE 3.
Merge pull request #27 from Gaerzi/master

Some DOSBox Raw OPL v2 indices were off by one.