size[0-3] are not initialized (and can get random negative trash
values), so the comparison with vs_total_ac_bits is messed up on the
first couple loop iterations, leading to AC underflows.
the b->prev pointers were not being maintained correctly. We
potentially have to update b->prev both before and after the area
whose VLC length is getting adjusted.
this also might fix the ppc regression failure?
patch by (Dan Maas <dmaas maasdigital com>)
Originally committed as revision 5064 to svn://svn.ffmpeg.org/ffmpeg/trunk