Music: Allow soundfonts without Mixer X (let Linux/OS X users use soundfonts)
This merge may let Linux/OSX users use custom soundfonts, even if they don't have SDL Mixer X.
I haven't tested it on those systems, but this code does work on Web. Please test on those systems. You must already have MIDI working on a regular build. You probably need Fluidsynth installed as your MIDI backend.
Edited by mazmazz