avformat/utils: Fix bitrate overflow check

The check added in df33a58e53 does not work
at all, rather it broke the summing of bitrates completely.
The comparission was wrong way around.
This commit replaces it by a simpler and hopefully clearer check

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

libavformat/utils.c

@@ -2219,18 +2219,15 @@ static void estimate_timings_from_bit_rate(AVFormatContext *ic)
 
     /* if bit_rate is already set, we believe it */
     if (ic->bit_rate <= 0) {
-        int bit_rate = 0;
+        int64_t bit_rate = 0;
         for(i=0;i<ic->nb_streams;i++) {
             st = ic->streams[i];
             if (st->codec->bit_rate > 0) {
-                if (INT_MAX - st->codec->bit_rate > bit_rate) {
-                    bit_rate = 0;
-                    break;
-                }
                 bit_rate += st->codec->bit_rate;
             }
         }
-        ic->bit_rate = bit_rate;
+        if (bit_rate <= INT_MAX)
+            ic->bit_rate = bit_rate;
     }
 
     /* if duration is already set, we believe it */