The AGOS PC-98 MIDI driver did not check the native_mt32 flag when determining
the type of MIDI device. This would cause a hardware MT-32 or external
softsynth to be treated as a GM device.
This commit fixes this by adding the missing check.
I have also made the necessary changes to the PC-98 audio drivers which were written to work around the current situation, but now also need a different order in the destructors.