avcodec/smacker: Check that the data size is a multiple of a sample vector

Fixes out of array access
Fixes: ce19e41f0ef1e52a23edc488faecdb58/asan_heap-oob_2504e97_4202_ffa0df1baed14022b9bfd4f8ac23d0cb.smk

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/smacker.c

@@ -670,6 +670,10 @@ static int smka_decode_frame(AVCodecContext *avctx, void *data,
 
     /* get output buffer */
     frame->nb_samples = unp_size / (avctx->channels * (bits + 1));
+    if (unp_size % (avctx->channels * (bits + 1))) {
+        av_log(avctx, AV_LOG_ERROR, "unp_size %d is odd\n", unp_size);
+        return AVERROR(EINVAL);
+    }
     if ((ret = ff_get_buffer(avctx, frame, 0)) < 0)
         return ret;
     samples  = (int16_t *)frame->data[0];