Currently the media source emit a presentation timestamp relative to
when the playback was last restarted. I.e., the frame that sits two
seconds inside a media file will get timestamp 2 if playback was
started at the beginning of the file, but will get timestamp 1 if
playback was last restarted at second 1.

This does not match Windows behavior, where each frame always gets
the same timestamp independently from where playback was started.
Signed-off-by: Giovanni Mascellani <gmascellani@codeweavers.com>
Signed-off-by: Huw Davies <huw@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>