avformat/mov: restrict unix timestamp hack to version 0 mdhd/mvhd

Commit 23eeffcd48 added a hack to support invalid
files where the creation date was encoded as a classic unix timestamp. Let's
reduce the scope of the hack by only applying it to version 0 mdhd/mvhd atoms.
Also warn the user of such possibly broken files.

Signed-off-by: Marton Balint <cus@passwd.hu>

libavformat/mov.c

@@ -1524,10 +1524,13 @@ static void mov_metadata_creation_time(MOVContext *c, AVIOContext *pb, AVDiction
     } else {
         time = avio_rb32(pb);
         avio_rb32(pb); /* modification time */
+        if (time > 0 && time < 2082844800) {
+            av_log(c->fc, AV_LOG_WARNING, "Detected creation time before 1970, parsing as unix timestamp.\n");
+            time += 2082844800;
+        }
     }
     if (time) {
-        if (time >= 2082844800)
-            time -= 2082844800;  /* seconds between 1904-01-01 and Epoch */
+        time -= 2082844800;  /* seconds between 1904-01-01 and Epoch */
 
         if ((int64_t)(time * 1000000ULL) / 1000000 != time) {
             av_log(c->fc, AV_LOG_DEBUG, "creation_time is not representable\n");