allow av_parser_close(NULL)

fixes issue300


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@13410 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/parser.c

@@ -214,10 +214,12 @@ int av_parser_change(AVCodecParserContext *s,
 
 void av_parser_close(AVCodecParserContext *s)
 {
+    if(s){
     if (s->parser->parser_close)
         s->parser->parser_close(s);
     av_free(s->priv_data);
     av_free(s);
+    }
 }
 
 /*****************************************************/