From 7f4eb4f6c6437ba60d3206d990dde5f006e6b44b Mon Sep 17 00:00:00 2001
From: Manfred Georg <manfred.georg@gmail.com>
Date: Fri, 26 Sep 2014 09:44:25 -0700
Subject: [PATCH] set ffmpeg mutex to NULL on destruction.

The Mutex manager registered with ffmpeg must reset the mutex to NULL after destruction, otherwise ffmpeg will give the invalid mutex to the next mutex manager when it asks it to CREATE a new mutex.
See ffmpeg code: http://git.videolan.org/?p=ffmpeg.git;a=blob;f=libavcodec/utils.c;h=28c5785398fcf11a3d3c70a8cd09e9df798e2734;hb=HEAD#l3423

Cherry picked from head (file has moved but issue is the same).
Conflicts:
	modules/videoio/src/cap_ffmpeg_impl.hpp
---
 modules/highgui/src/cap_ffmpeg_impl.hpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/modules/highgui/src/cap_ffmpeg_impl.hpp b/modules/highgui/src/cap_ffmpeg_impl.hpp
index be9c7aa3e2..5f0207c165 100644
--- a/modules/highgui/src/cap_ffmpeg_impl.hpp
+++ b/modules/highgui/src/cap_ffmpeg_impl.hpp
@@ -485,6 +485,7 @@ static int LockCallBack(void **mutex, AVLockOp op)
             localMutex->destroy();
             free(localMutex);
             localMutex = NULL;
+            *mutex = NULL;
         break;
     }
     return 0;