Vorbis specs requires blocksize_1 >= blocksize_0, error if it's false.

Predict buffer size from blocksize_1 and number of channels and make
sure this does not exceed AVCODEC_MAX_AUDIO_FRAME_SIZE

Patch by Uoti Urpala >>> uoti |.| urpala |@| pp1 |.| inet |.| fi <<<

Originally committed as revision 5313 to svn://svn.ffmpeg.org/ffmpeg/trunk