alac: fix integer overflow leading to subsequent out of array accesses.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/alac.c

@@ -542,7 +542,11 @@ static av_cold int alac_decode_close(AVCodecContext *avctx)
 static int allocate_buffers(ALACContext *alac)
 {
     int ch;
-    int buf_size = alac->max_samples_per_frame * sizeof(int32_t);
+    int buf_size;
+
+    if (alac->max_samples_per_frame > INT_MAX / sizeof(int32_t))
+        goto buf_alloc_fail;
+    buf_size = alac->max_samples_per_frame * sizeof(int32_t);
 
     for (ch = 0; ch < FFMIN(alac->channels, 2); ch++) {
         FF_ALLOC_OR_GOTO(alac->avctx, alac->predict_error_buffer[ch],