ffplay: use frame->pkt_pts instead of pkt->pts in audio pts calculation

Fixes ticket #2717.

Signed-off-by: Marton Balint <cus@passwd.hu>
ffplay: always send zero packets to flush audio decoders

Zero packets are needed not for codecs with CODEC_CAP_DELAY but for
multithreaded decoders as well.

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

* cus/stable:
  ffplay: always send zero packets to flush audio decoders
  ffplay: use frame->pkt_pts instead of pkt->pts in audio pts calculation

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