movenc: support an alternative to edit lists to handle the first DTS != 0 case.

Some software does not support edit lists at all, the adobe flash
player seems to be one of these. Which results in AV sync errors when
edit lists are used to adjust AV sync.

2nd try on implementing this, the first try had various issues

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>