Log Message:
fluidsynth: update to 2.1.6.

SoundFonts may never be unloaded correctly, if

    polyphony is ever exceeded (#727), or
    voices are still playing while their SoundFont is being unloaded.

Calling delete_fluid_synth() does not free those SoundFonts either. Affected are \ 
versions from 1.1.4 to 2.1.5 .
Other bug-fixes:

    fix a heap-based use-after-free (#733)