In some ISO-BMFF files, there is an initial non-zero composition offset,
but there is no EditList present.
This is against ISO-BMFF spec recommentation [1] and we believe in most
cases it is just missing the EditList.
[1] 14496-12:2015 8.6.6.1
It is recommended that such an edit be used to establish a presentation
time of 0 for the first presented sample, when composition offsets are
used.
Issue: #112.
Fixes: b/110782437.
Change-Id: I23d33810ce536b09a1e22a2644828d824c1314f5
KongQun Yang