dvdplayer: use startpts as a time reference if no other is available

This avoids display of wrong time after seek, due to lack of timestamps
dvdplayer: remove code that set limit on smallest frame rate

This skips the "slow" motion video after seek, by instead starting
playback when next frame is to be displayed
dvdplayer: always output the first frame after seek/startup without wait

This make sure we get something new on display after seek, even if
the next frame is to be displayed sometime later
dvdplayer: avoid busy waiting for video renderers to get a buffer
coreae: when a flush is requested delay is zero

On seek, the flush was requested, but not performed when delay
was requested, leading to stuttering on seek.
Merge pull request #4051 from elupus/seekframe

Seekframe