avformat/aiffdec: Use 64bit for block_duration use

Fixes: signed integer overflow: 3 * -2147483648 cannot be represented in type 'int'
Fixes: 50993/clusterfuzz-testcase-minimized-ffmpeg_dem_AIFF_fuzzer-6668935979728896

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

libavformat/aiffdec.c

@@ -428,7 +428,7 @@ static int aiff_read_packet(AVFormatContext *s,
         pkt->flags &= ~AV_PKT_FLAG_CORRUPT;
     /* Only one stream in an AIFF file */
     pkt->stream_index = 0;
-    pkt->duration     = (res / st->codecpar->block_align) * aiff->block_duration;
+    pkt->duration     = (res / st->codecpar->block_align) * (int64_t) aiff->block_duration;
     return 0;
 }