matroskadec: minor simplification

patch from reimar

Originally committed as revision 24804 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/matroskadec.c

@@ -1734,7 +1734,7 @@ static int matroska_parse_block(MatroskaDemuxContext *matroska, uint8_t *data,
                 int offset = 0, pkt_size = lace_size[n];
                 uint8_t *pkt_data = data;
 
-                if (lace_size[n] > size) {
+                if (pkt_size > size) {
                     av_log(matroska->ctx, AV_LOG_ERROR, "Invalid packet size\n");
                     break;
                 }