set ffmpeg mutex to NULL on destruction.

diff --git a/modules/videoio/src/cap_ffmpeg_impl.hpp b/modules/videoio/src/cap_ffmpeg_impl.hpp
index 4a3b029..02aeec0 100644 (file)
--- a/modules/videoio/src/cap_ffmpeg_impl.hpp
+++ b/modules/videoio/src/cap_ffmpeg_impl.hpp
@@ -493,6 +493,7 @@ static int LockCallBack(void **mutex, AVLockOp op)
             localMutex->destroy();
             free(localMutex);
             localMutex = NULL;
+            *mutex = NULL;
         break;
     }
     return 0;