avcodec/wmalosslessdec: Check block_align maximum

Fixes: Assertion failure
Fixes: 22737/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_WMALOSSLESS_fuzzer-5958388889681920

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 314d10f7a6)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/wmalosslessdec.c

@@ -184,7 +184,7 @@ static av_cold int decode_init(AVCodecContext *avctx)
     unsigned int channel_mask;
     int i, log2_max_num_subframes;
 
-    if (avctx->block_align <= 0) {
+    if (avctx->block_align <= 0 || avctx->block_align > (1<<21)) {
         av_log(avctx, AV_LOG_ERROR, "block_align is not set or invalid\n");
         return AVERROR(EINVAL);
     }