avformat/utils: limit rfps to values larger than fps

This avoids some nonsense values being produced by totally corrupted input

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

libavformat/avformat.h

@@ -756,6 +756,7 @@ typedef struct AVStream {
         int64_t last_dts;
         int64_t duration_gcd;
         int duration_count;
+        int64_t rfps_duration_sum;
         double (*duration_error)[2][MAX_STD_TIMEBASES];
         int64_t codec_info_duration;
         int64_t codec_info_duration_fields;