fix build against glib<2.30
fix build against glib<2.30

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