avformat/mpegts: check sl.timestamp_len

Fixes: msan_uninit-mem_7ff4404547ba_4883_dmbts.ts
Fixes assertion failure
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mpegts.c

@@ -1256,6 +1256,11 @@ static int parse_MP4SLDescrTag(MP4DescrParseContext *d, int64_t off, int len)
         descr->sl.timestamp_res      = avio_rb32(&d->pb);
                                        avio_rb32(&d->pb);
         descr->sl.timestamp_len      = avio_r8(&d->pb);
+        if (descr->sl.timestamp_len > 64) {
+            avpriv_request_sample(NULL, "timestamp_len > 64");
+            descr->sl.timestamp_len = 64;
+            return AVERROR_PATCHWELCOME;
+        }
         descr->sl.ocr_len            = avio_r8(&d->pb);
         descr->sl.au_len             = avio_r8(&d->pb);
         descr->sl.inst_bitrate_len   = avio_r8(&d->pb);