avformat/kvag: Fix integer overflow in bitrate computation

Fixes: signed integer overflow: 1077952576 * 4 cannot be represented in type 'int'
Fixes: 26152/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5674758518341632

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

libavformat/kvag.c

@@ -83,7 +83,7 @@ static int kvag_read_header(AVFormatContext *s)
     par->bits_per_raw_sample    = 16;
     par->block_align            = 1;
     par->bit_rate               = par->channels *
-                                  par->sample_rate *
+                                  (uint64_t)par->sample_rate *
                                   par->bits_per_coded_sample;
 
     avpriv_set_pts_info(st, 64, 1, par->sample_rate);