ffplay: do not wait for flushing the picture queue on flush packet

It is no longer necessary. Also do frame timer and video current pos reset in
the main thread because with the wait removed, the timing would not be optimal
in the read thread.

Signed-off-by: Marton Balint <cus@passwd.hu>
ffplay: remove no longer necessary codec flush

It was introduced in c2e8691c07ca52de7b6b00ba8f2b30c56fd786d7, but since we no
longer no longer provide a custom get_buffer callback, the original cause of
the issue is gone.

Signed-off-by: Marton Balint <cus@passwd.hu>
ffplay: factor out function setting default window size

Signed-off-by: Marton Balint <cus@passwd.hu>
ffplay: set default window size before starting audio

Fixes ticket #2381.

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

* cus/stable:
  ffplay: set default window size before starting audio
  ffplay: factor out function setting default window size
  ffplay: remove no longer necessary codec flush
  ffplay: do not wait for flushing the picture queue on flush packet

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