ogg_afh.c: Switch to ogg vorbis callbacks

ogg_afh.c: Switch to ogg vorbis callbacks

This allows to call ov_clear() already during ogg_get_file_info() which
in turn simplifies ogg_close_audio_file().

This is a preparation for moving the close function of the audio
format handlers to the virtual streaming system as they all do
essentially the same now.