avformat/asfdec_f: Change order or operations slightly

Fixes: signed integer overflow: 20 * 5184056935931942919 cannot be represented in type 'long'
Fixes: 25466/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-4798660247552000

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

libavformat/asfdec_f.c

@@ -424,7 +424,7 @@ static int asf_read_stream_properties(AVFormatContext *s, int64_t size)
     if (!(asf->hdr.flags & 0x01)) { // if we aren't streaming...
         int64_t fsize = avio_size(pb);
         if (fsize <= 0 || (int64_t)asf->hdr.file_size <= 0 ||
-            20*FFABS(fsize - (int64_t)asf->hdr.file_size) < FFMIN(fsize, asf->hdr.file_size))
+            FFABS(fsize - (int64_t)asf->hdr.file_size) < FFMIN(fsize, asf->hdr.file_size)/20)
             st->duration = asf->hdr.play_time /
                        (10000000 / 1000) - start_time;
     }