matroskadec: sanitize track time_scale before using it

fix issue628


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@15280 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/matroskadec.c

@@ -1274,6 +1274,8 @@ static int matroska_read_header(AVFormatContext *s, AVFormatParameters *ap)
             av_log(matroska->ctx, AV_LOG_INFO,
                    "Unknown/unsupported CodecID %s.\n", track->codec_id);
 
+        if (track->time_scale < 0.01)
+            track->time_scale = 1.0;
         av_set_pts_info(st, 64, matroska->time_scale*track->time_scale, 1000*1000*1000); /* 64 bit pts in ns */
 
         st->codec->codec_id = codec_id;