Audio artefact fix

This will probably help minimize the audio issues on windows. Since the comment in PSPMixer says (// Our dsound backend will not stop playing), I just adopted the same technique. If __sceDoMix() is unable to acquire a lock, NativeApp writes zeroes onto the audio buffer. This (technically) should stop audio from repeatedly playing the same thing over and over again. 

I haven't tested this (I don't own a windows machine), So I'd be glad it someone tries this out.