Filip Roséen authored Jul 17, 2016 and Rémi Denis-Courmont committed Jul 17, 2016

This patch fixes a crash when trying to invoke avcodec_flush_buffers
on an not-yet-opened AvCodecContext*.

The previous if-condition is faulty because nothing guarantees that
the state of the variable in question reflects whether we are in a
state where p_sys->p_context is valid; instead it has been
replaced by a call to "avcodec_is_open".

refs: #17080

--

"p_sys->p_context" is opened (through avcodec_open2) in "ffmpeg_OpenCodec",
which is not guaranteed to have been called prior to "EndVideoDec" (due to
potential missing data required for codec initialization).

See the implementation of OpenVideoCodec in codec/avcodec/video.c for more
information.

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>