mov: add workaround for incorrect 0 time point.

Fixes Ticket1471
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mov.c

@@ -780,7 +780,8 @@ static void mov_metadata_creation_time(AVDictionary **metadata, time_t time)
     char buffer[32];
     if (time) {
         struct tm *ptm;
-        time -= 2082844800;  /* seconds between 1904-01-01 and Epoch */
+        if(time >= 2082844800)
+            time -= 2082844800;  /* seconds between 1904-01-01 and Epoch */
         ptm = gmtime(&time);
         if (!ptm) return;
         strftime(buffer, sizeof(buffer), "%Y-%m-%d %H:%M:%S", ptm);