avformat/utils: fix memory leak in avformat_free_context

The pointer to the packet queue is stored in the internal structure
so the queue needs to be flushed before internal is freed.

Signed-off-by: Steven Siloti <ssiloti@bittorrent.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 949debd1d1)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/utils.c

@@ -4199,8 +4199,8 @@ void avformat_free_context(AVFormatContext *s)
     av_dict_free(&s->metadata);
     av_dict_free(&s->internal->id3v2_meta);
     av_freep(&s->streams);
-    av_freep(&s->internal);
     flush_packet_queue(s);
+    av_freep(&s->internal);
     av_free(s);
 }