avformat/iff: Use 64bit in duration computation

Fixes: signed integer overflow: 588 * 16719904 cannot be represented in type 'int'
Fixes: 29102/clusterfuzz-testcase-minimized-ffmpeg_dem_IFF_fuzzer-6748331936186368

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

libavformat/iff.c

@@ -384,7 +384,7 @@ static int read_dst_frame(AVFormatContext *s, AVPacket *pkt)
                 avio_skip(pb, 1);
             pkt->flags |= AV_PKT_FLAG_KEY;
             pkt->stream_index = 0;
-            pkt->duration = 588 * s->streams[0]->codecpar->sample_rate / 44100;
+            pkt->duration = 588LL * s->streams[0]->codecpar->sample_rate / 44100;
             pkt->pos = chunk_pos;
 
             chunk_pos = avio_tell(pb);