If AVPacket->data == NULL, the packet does not contain any buffer to

be freed.
This fixes a double free on exit.

Originally committed as revision 16857 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavdevice/v4l2.c

@@ -325,6 +325,10 @@ static void mmap_release_buffer(AVPacket *pkt)
     int res, fd;
     struct buff_data *buf_descriptor = pkt->priv;
 
+    if (pkt->data == NULL) {
+         return;
+    }
+
     memset(&buf, 0, sizeof(struct v4l2_buffer));
     buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
     buf.memory = V4L2_MEMORY_MMAP;