[Bug 40024] Prosound crashes on start

https://bugs.winehq.org/show_bug.cgi?id=40024

--- Comment #4 from Andrew Eikum  ---
To elaborate a bit more, the application calls midiOutPrepareHeader, which
allocates a 32-bit backing header. Then the application calls MODM_LONGDATA
with that header, so mmsystem16 maps the header to the backing header and
invokes 32-bit winmm.  Eventually this calls the application's MOM_DONE
callback with that header. The application calls midiOutUnprepareHeader during
this callback, which frees the 32-bit backing header. After the callback is
done, the LONGDATA call unmaps its 32-bit header, but this was deleted by the
UnprepareHeader call, and the application crashes.