avformat/rtpdec_mpeg4: Use av_freep() to avoid leaving stale pointers in memory

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/rtpdec_mpeg4.c

@@ -95,9 +95,9 @@ static PayloadContext *new_context(void)
 
 static void free_context(PayloadContext *data)
 {
-    av_free(data->au_headers);
-    av_free(data->mode);
-    av_free(data);
+    av_freep(&data->au_headers);
+    av_freep(&data->mode);
+    av_freep(&data);
 }
 
 static int parse_fmtp_config(AVCodecContext *codec, char *value)