fix slice header parsing in AVC essence parser
fix slice header parsing in AVC essence parser

xunchangguo/BMX,Limecraft/ebu-bmx,Limecraft/ebu-bmx,kierank/bmxlib-bmx,Limecraft/ebu-bmx,xunchangguo/BMX,kierank/bmxlib-bmx,stuarthicks/bmx,stuarthicks/bmx,stuarthicks/bmx,kierank/bmxlib-bmx,xunchangguo/BMX