Fix #7189: Fluidsynth volume gain too high

[nikolas]

No description provided.

[nielsmh]

I'm impressed the gain range for fluidsynth is 0.0 to 10.0, default is 0.2, and anything above that easily causes clipping.

Would it be too much to ask to make it a configurable setting for the music driver, similar to how the Win32 and DMusic drivers allows selecting a MIDI port? Users would only be able to configure it via commandline or editing the ini file, but still an option for advanced users who may be using a different sound font with different volume characteristics.

[nielsmh]

Can't see anything straight up wrong with this. If anyone complains about too low volume we can implement a configuration for max gain at that time.

[nielsmh]

Let me be the one to complain about low volume. The music is way too soft compared to sound effects at this level.