vorbis 5:1 decoding fix, fix mi2_vorbis51.mp4, patch by Denes Balatoni...

vorbis 5:1 decoding fix, fix mi2_vorbis51.mp4, patch by Denes Balatoni <dbalatoni at programozo dot hu>

Originally committed as revision 5349 to svn://svn.ffmpeg.org/ffmpeg/trunk