Seek cause a deadlock

Since 9ba5f88e, seek causes a deadlock on regular h264 content with multi threaded decoding.

Tested on android, win32 and mac.

Maybe there's no bug in vlc itself and the commit is just revealing a bug in libav, but the fact is seeking is broken since this commit.

assigned to @Courmisch

changed milestone to %2.2.x maintenance branch

added Status::fixed label

closed

commit 19c16247 Author: Rémi Denis-Courmont remi@remlab.net Date: Wed Jul 3 21:51:23 2013 +0300

avcodec: fix deadlock when flusing (fixes [#8901](https://code.videolan.org/videolan/vlc/-/issues/8901))

avcodec_flush_buffers() may get or release frame buffers.
See also EndVideoDec().

Original author: remi@remlab.net