avformat/concatdec: Check in/outpoint for overflow

Fixes: signed integer overflow: 91542414454000000 - -9154241494546000000 cannot be represented in type 'long'
Fixes: 51896/clusterfuzz-testcase-minimized-ffmpeg_dem_CONCAT_fuzzer-4739147999084544

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>

libavformat/concatdec.c

@@ -667,7 +667,9 @@ static int concat_read_header(AVFormatContext *avf)
         else
             time = cat->files[i].start_time;
         if (cat->files[i].user_duration == AV_NOPTS_VALUE) {
-            if (cat->files[i].inpoint == AV_NOPTS_VALUE || cat->files[i].outpoint == AV_NOPTS_VALUE)
+            if (cat->files[i].inpoint == AV_NOPTS_VALUE || cat->files[i].outpoint == AV_NOPTS_VALUE ||
+                cat->files[i].outpoint - (uint64_t)cat->files[i].inpoint != av_sat_sub64(cat->files[i].outpoint, cat->files[i].inpoint)
+            )
                 break;
             cat->files[i].user_duration = cat->files[i].outpoint - cat->files[i].inpoint;
         }