avformat/timecode: use 64bit for intermediate for rounding in fps_from_frame_rate()

Fixes: 62276/clusterfuzz-testcase-minimized-ffmpeg_dem_MOV_fuzzer-4802790784303104
Fixes: signed integer overflow: 1768972133 + 968491058 cannot be represented in type 'int'

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/timecode.c

@@ -210,7 +210,7 @@ static int fps_from_frame_rate(AVRational rate)
 {
     if (!rate.den || !rate.num)
         return -1;
-    return (rate.num + rate.den/2) / rate.den;
+    return (rate.num + rate.den/2LL) / rate.den;
 }
 
 int av_timecode_check_frame_rate(AVRational rate)