avformat/swfenc: Fix integer overflow in frame rate handling

Fixes: signed integer overflow: 30000299 * 256 cannot be represented in type 'int'
Fixes: ticket8184

Found-by: Suhwan
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/swfenc.c

@@ -256,7 +256,7 @@ static int swf_write_header(AVFormatContext *s)
         av_log(s, AV_LOG_ERROR, "Invalid (too large) frame rate %d/%d\n", rate, rate_base);
         return AVERROR(EINVAL);
     }
-    avio_wl16(pb, (rate * 256) / rate_base); /* frame rate */
+    avio_wl16(pb, (rate * 256LL) / rate_base); /* frame rate */
     swf->duration_pos = avio_tell(pb);
     avio_wl16(pb, (uint16_t)(DUMMY_DURATION * (int64_t)rate / rate_base)); /* frame count */