mxf reader: remove redundant check on precharge/rollout sign
mxf reader: remove redundant check on precharge/rollout sign

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