avformat/vpk: Fix integer overflow in samples_per_block computation

Fixes: signed integer overflow: 84026453 * 28 cannot be represented in type 'int'
Fixes: 15111/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5675630072430592

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

libavformat/vpk.c

@@ -56,12 +56,12 @@ static int vpk_read_header(AVFormatContext *s)
     st->codecpar->codec_id    = AV_CODEC_ID_ADPCM_PSX;
     st->codecpar->block_align = avio_rl32(s->pb);
     st->codecpar->sample_rate = avio_rl32(s->pb);
-    if (st->codecpar->sample_rate <= 0)
+    if (st->codecpar->sample_rate <= 0 || st->codecpar->block_align <= 0)
         return AVERROR_INVALIDDATA;
     st->codecpar->channels    = avio_rl32(s->pb);
     if (st->codecpar->channels <= 0)
         return AVERROR_INVALIDDATA;
-    samples_per_block      = ((st->codecpar->block_align / st->codecpar->channels) * 28) / 16;
+    samples_per_block      = ((st->codecpar->block_align / st->codecpar->channels) * 28LL) / 16;
     if (samples_per_block <= 0)
         return AVERROR_INVALIDDATA;
     vpk->block_count       = (st->duration + (samples_per_block - 1)) / samples_per_block;