DJ's first steps in C and vlc decoders ;)

DJ's first steps in C and vlc decoders ;)
* modules/audio_filter/converter/mpgatofixed32.c:
  - fixed an issue that could cause glitches when switching from one stream
    to another. the buffer wasn't entirely getting 0000 because multiple
    channels were not taken into account when doing this.
* ALL:
  - if float32 then clear the buffer with (float)0