avformat/mov: fix integer overflow in mov_read_udta_string()

Found-by: Paul Mehta <paul@paulmehta.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mov.c

@@ -375,7 +375,7 @@ static int mov_read_udta_string(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 
     if (!key)
         return 0;
-    if (atom.size < 0)
+    if (atom.size < 0 || str_size >= INT_MAX/2)
         return AVERROR_INVALIDDATA;
 
     // worst-case requirement for output string in case of utf8 coded input