hexter 2.7.2

An FB-01 bank saved as a MIDI file now loads

Every format hexter reads is looked for inside a .mid as well as in a bare .syx, because
saving a dump into a MIDI file is a normal thing to do and always has been. The FB-01 support
that shipped in 2.7.0 checked whole files only, so a bank wrapped that way was quietly
ignored: no error, just nothing.

It is recognized in the same scan as every other dump now, allowing for the length bytes a
MIDI file writes after the F0. That also means an FB-01 bank works in a file holding more than
one dump, and that its 48 voices arrive through the same path every other format uses.

Ignoring the shift fails only the MIDI-file checks; taking the FB-01 branch out of the scan
fails the FB-01 checks wholesale, including a load that quietly yields 49 voices of nothing.

DX7 output is unchanged, byte for byte against 2.5.1, in both the fixed-point and the
floating-point engine.