avcodec/atrac3: Check block_align

Fixes: Infinite loop
Fixes: 17620/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ATRAC3_fuzzer-5086123012915200

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegReviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/atrac3.c

@@ -964,7 +964,7 @@ static av_cold int atrac3_decode_init(AVCodecContext *avctx)
         return AVERROR_INVALIDDATA;
     }
 
-    if (avctx->block_align >= UINT_MAX / 2)
+    if (avctx->block_align >= UINT_MAX / 2 || avctx->block_align <= 0)
         return AVERROR(EINVAL);
 
     q->decoded_bytes_buffer = av_mallocz(FFALIGN(avctx->block_align, 4) +