windows: allow SF2 to be loaded from unicode paths
windows: allow SF2 to be loaded from unicode paths

fix #128

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