Revert "mpegts: do not set pts for missing dts in video streams"

This reverts commit f65afef1df49f53e14c8d4173ff960fff8d44ecb.

If only pts is coded then dts must be equal pts
See Rec. ITU-T H.222.0 (06/2012) / ISO/IEC 13818-1:2013 (E) 2.7.5

Found-by: Baptiste Coudurier