bmxtranswrap: allow ess marks in input's precharge
bmxtranswrap: allow ess marks in input's precharge

last_ess_mark_pos was initialized to -1 which meant that essence
marks in input frames with position < 0 would be ignored. Changed
the init to INT64_MIN

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