bmxtranswrap: seek to start when setting read limits
bmxtranswrap: seek to start when setting read limits

The seek call before reading samples is not required and was also
wrong because it didn't take into account precharge. This resulted
in the clip duration being < output duration for some mpeg2 lg
sequences

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