Fixed can't play a link which have both SegmentBase and SegmentTemplate.
Created by: oldmtn
// Issue Can't play test link http://vm2.dashif.org/livesim-dev/periods_0/peroff_1/testpic_2s/Manifest.mpd
// Root Cause This link have both SegmentBase and SegmentTemplate.
// Solution And we should merge properites of SegmentBase to SegmentTemplate. I add a special case to handle this situation.