Update fluidsynth to 2.0.8
- Fix incorrect behavior of fluid_sample_set_sound_data().
- Fix voices being mixed incorrectly, causing audible crackle esp. at sample-rates >48kHz.
- Make sure that defining NDEBUG disables assertions.
Test Plan: - Checked that qsynth worked as expected.
Reviewers: Triage Team, JoshStrobl
Reviewed By: Triage Team, JoshStrobl
Differential Revision: https://dev.getsol.us/D7508