FACTWaveBank_Destroy will invoke the callback which we
attempt to lookup the wavebank.
The callback must have a pointer, help states it isn't valid but still
points to the wavebank that was destroyed.
Signed-off-by: Alistair Leslie-Hughes <leslie_alistair(a)hotmail.com>
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https://gitlab.winehq.org/wine/wine/-/merge_requests/517