avcodec/alsdec: Fix integer overflow with buffer number

Fixes: signed integer overflow: 65313 * 65313 cannot be represented in type 'int'
Fixes: 15290/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALS_fuzzer-5738074249625600

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 5f64f6058e)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/alsdec.c

@@ -1733,6 +1733,8 @@ static av_cold int decode_init(AVCodecContext *avctx)
 
     // allocate quantized parcor coefficient buffer
     num_buffers = sconf->mc_coding ? avctx->channels : 1;
+    if (num_buffers * (uint64_t)num_buffers > INT_MAX) // protect chan_data_buffer allocation
+        return AVERROR_INVALIDDATA;
 
     ctx->quant_cof        = av_malloc_array(num_buffers, sizeof(*ctx->quant_cof));
     ctx->lpc_cof          = av_malloc_array(num_buffers, sizeof(*ctx->lpc_cof));