SIDX based playback is not restricted to SegmentBase, but it possible
with SegmentList/SegmentTemplate. In the latter case, each fragment
has its own SIDX box and might be subdivided into subfragment.
So, demux should not assume that the end of subfragment is the end
of stream. Moreover, should try advance subfragment only if there
are remaining subfragments.
With additional fixes by Sebastian Dröge <sebastian@centricular.com>
https://bugzilla.gnome.org/show_bug.cgi?id=776200
a9c34fb9e3