mov: fix decode of fragments that overlap in time

mov: fix decode of fragments that overlap in time

When keyframe intervals of dash segments are not perfectly aligned,
fragments in the stream can overlap in time. The previous sorting by
timestamp causes packets to be read out of decode order and results
in decode errors.

Insert new "trun" index entries into index_entries in the order that
the trun are referenced by the sidx.

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>