[omxplayer] Use display time for EDL cut start time

There are reports that EDL commercial break skipping occurs 5-10 seconds too early. This is because the skip occurs when a timestamp
is received at PlayerVideo/PlayerAudio, but it may still be a number of seconds before that frame is presented by the GPU.

Instead use the display time (GetTime) to determine start of cut time
[omxplayer] Don't fail to open a stream with zero dimensions

The fast channel switching mod means OMXVideo may be opened before hints.width/hints/width is valid.
If we fail here, we do get opened again when the width/height are available, but we have already skipped
some init code like openeing the EDL files. Behave more like dvdplayer and ignore the zero dimensions.