Use av_freep() in ff_parse_close().

Originally committed as revision 15654 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/parser.c

@@ -291,7 +291,7 @@ void ff_parse_close(AVCodecParserContext *s)
 {
     ParseContext *pc = s->priv_data;
 
-    av_free(pc->buffer);
+    av_freep(&pc->buffer);
 }
 
 void ff_parse1_close(AVCodecParserContext *s)