avformat/hlsenc: Free context after hls_append_segment

Fixes reading uninitialized memory

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 530eb6acf8)

Conflicts:

	libavformat/hlsenc.c
(cherry picked from commit 0ac22f043b)

Conflicts:

	libavformat/hlsenc.c

libavformat/hlsenc.c

@@ -314,9 +314,10 @@ static int hls_write_trailer(struct AVFormatContext *s)
 
     av_write_trailer(oc);
     avio_closep(&oc->pb);
-    avformat_free_context(oc);
     av_free(hls->basename);
     append_entry(hls, hls->duration);
+    avformat_free_context(oc);
+    hls->avf = NULL;
     hls_window(s, 1);
 
     free_entries(hls);