h264dump: simplify next_bits and fix potential >56 bit issue
h264dump: simplify next_bits and fix potential >56 bit issue

If the number of bits required is > 56 then potentially 9 bytes
are required in the shifting process. The previous code didn't take this
into account and the MSB bits could have been lost

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