wmaprodec: tighter check for num_vec_coeffs

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

libavcodec/wmaprodec.c

@@ -1166,6 +1166,7 @@ static int decode_subframe(WMAProDecodeCtx *s)
             transmit_coeffs = 1;
     }
 
+    av_assert0(s->subframe_len <= WMAPRO_BLOCK_MAX_SIZE);
     if (transmit_coeffs) {
         int step;
         int quant_step = 90 * s->bits_per_sample >> 4;
@@ -1176,7 +1177,7 @@ static int decode_subframe(WMAProDecodeCtx *s)
             for (i = 0; i < s->channels_for_cur_subframe; i++) {
                 int c = s->channel_indexes_for_cur_subframe[i];
                 int num_vec_coeffs = get_bits(&s->gb, num_bits) << 2;
-                if (num_vec_coeffs > WMAPRO_BLOCK_MAX_SIZE) {
+                if (num_vec_coeffs > s->subframe_len) {
                     av_log(s->avctx, AV_LOG_ERROR, "num_vec_coeffs %d is too large\n", num_vec_coeffs);
                     return AVERROR_INVALIDDATA;
                 }