avformat/xwma: Use av_rescale() for duration computation

Fixes: signed integer overflow: 34242363648 * 538976288 cannot be represented in type 'long'
Fixes: 50993/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-6577923913547776

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

libavformat/xwma.c

@@ -278,7 +278,7 @@ static int xwma_read_header(AVFormatContext *s)
          * the total duration using the average bits per sample and the
          * total data length.
          */
-        st->duration = (size<<3) * st->codecpar->sample_rate / st->codecpar->bit_rate;
+        st->duration = av_rescale((size<<3), st->codecpar->sample_rate, st->codecpar->bit_rate);
     }
 
 fail: