collectpads: Assume PTS is equal DTS if PTS is missing
collectpads: Assume PTS is equal DTS if PTS is missing

This is the best guess we can make if such a buffer reached the collect
pad. This is uncommon, we do expect parsers to have tried and fixed that
if possible (or needed).

https://bugzilla.gnome.org/show_bug.cgi?id=762207

StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer