ffplay: fix early frame dropped pts serial

Fixes early frame drop which was kind of broken since
26c208cf0ff59efd7786528884a64d35fc42e9bf.

Signed-off-by: Marton Balint <cus@passwd.hu>
ffplay: always queue attachment pictures after flushing the video packet queue

Requeue them after seeking and also after opening a video stream. Also don't
fill the video queue in case of an attached picture video stream since there
will be no more than one packet from that stream.

Signed-off-by: Marton Balint <cus@passwd.hu>
Merge remote-tracking branch 'cus/stable'

* cus/stable:
  ffplay: always queue attachment pictures after flushing the video packet queue
  ffplay: fix early frame dropped pts serial

Merged-by: Michael Niedermayer <michaelni@gmx.at>