avformat/sbgdec: Check for negative duration or un-representable end pts

Fixes: signed integer overflow: 9230955872951340 - -9223372036854775808 cannot be represented in type 'long'
Fixes: 51896/clusterfuzz-testcase-minimized-ffmpeg_dem_SBG_fuzzer-6330481893572608

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 9b00b5734d)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/sbgdec.c

@@ -1461,6 +1461,13 @@ static av_cold int sbg_read_header(AVFormatContext *avf)
     st->duration      = script.end_ts == AV_NOPTS_VALUE ? AV_NOPTS_VALUE :
                         av_rescale(script.end_ts - script.start_ts,
                                    sbg->sample_rate, AV_TIME_BASE);
+
+    if (st->duration != AV_NOPTS_VALUE && (
+        st->duration < 0 || st->start_time > INT64_MAX - st->duration)) {
+        r = AVERROR_INVALIDDATA;
+        goto fail;
+    }
+
     sti->cur_dts      = st->start_time;
     r = encode_intervals(&script, st->codecpar, &inter);
     if (r < 0)