avformat/mov: creation time should be non negative

Fixes: signed integer overflow: -9223372036854775808 - 2082844800 cannot be represented in type 'long'
Fixes: 58384/clusterfuzz-testcase-minimized-ffmpeg_dem_MOV_fuzzer-6428383700713472

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mov.c

@@ -1521,6 +1521,10 @@ static void mov_metadata_creation_time(MOVContext *c, AVIOContext *pb, AVDiction
     if (version == 1) {
         time = avio_rb64(pb);
         avio_rb64(pb);
+        if (time < 0) {
+            av_log(c->fc, AV_LOG_DEBUG, "creation_time is negative\n");
+            return;
+        }
     } else {
         time = avio_rb32(pb);
         avio_rb32(pb); /* modification time */