Initialize newly allocated channel map with a value of -1 (off) for all channels.
Initialize newly allocated channel map with a value of -1 (off) for all channels.

https://github.com/FluidSynth/fluidsynth/pull/1081#discussion_r853430986

FluidSynth/fluidsynth,FluidSynth/fluidsynth,FluidSynth/fluidsynth,FluidSynth/fluidsynth