wmaenc: limit block_align to MAX_CODED_SUPERFRAME_SIZE

This is near the theoretical limit for wma frame size and is the most that
our decoder can handle. Allowing higher bit rates will just end up padding
each frame with empty bytes.

Fixes invalid writes for avconv when using very high bit rates.

CC:libav-stable@libav.org

libavcodec/wmaenc.c

@@ -71,8 +71,12 @@ static int encode_init(AVCodecContext * avctx){
     for(i = 0; i < s->nb_block_sizes; i++)
         ff_mdct_init(&s->mdct_ctx[i], s->frame_len_bits - i + 1, 0, 1.0);
 
-    avctx->block_align=
-    s->block_align= avctx->bit_rate*(int64_t)s->frame_len / (avctx->sample_rate*8);
+    s->block_align     = avctx->bit_rate * (int64_t)s->frame_len /
+                         (avctx->sample_rate * 8);
+    s->block_align     = FFMIN(s->block_align, MAX_CODED_SUPERFRAME_SIZE);
+    avctx->block_align = s->block_align;
+    avctx->bit_rate    = avctx->block_align * 8LL * avctx->sample_rate /
+                         s->frame_len;
 //av_log(NULL, AV_LOG_ERROR, "%d %d %d %d\n", s->block_align, avctx->bit_rate, s->frame_len, avctx->sample_rate);
     avctx->frame_size= s->frame_len;