Fix DVB and PGS subtitles after 733bc17aaed8751565c5343c9b0e7ecce96c2796.

The timings were wrong after the first seek.

Simplify the code to use real timing for all subtitle types.
DVB subtitles: Try to make some sense out of the PTS parsing code.

Also fix a typo which had no effect on the execution and remove member variables that were used only in one function.

Fixes CID 1233585.
Subtitle pin: Remove a redundant check.

pData can't be null by construction and checking the size is enough anyway.

Fixes CID 1233586.
PGS Subtitles: Ignore empty segments again now that the subtitle queue is fixed.

e664bace0fb7d5feecd0ed460c6b49f80916bd57 added the needed framework on the subtitle queue side.