mxf reader: check samples rates in max precharge/rollout method
mxf reader: check samples rates in max precharge/rollout method

The code currently assumes that when an external reader has non-zero
precharge or rollout that the external reader's sample rate equals
the parent reader's sample rate

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