avcodec/ra288: Check block_align for the assumed value

Fixes: Timeout (224sec -> 1ms)
Fixes: 18408/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_RA_288_fuzzer-5740382570151936

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

libavcodec/ra288.c

@@ -77,7 +77,7 @@ static av_cold int ra288_decode_init(AVCodecContext *avctx)
     avctx->channel_layout = AV_CH_LAYOUT_MONO;
     avctx->sample_fmt     = AV_SAMPLE_FMT_FLT;
 
-    if (avctx->block_align <= 0) {
+    if (avctx->block_align != 38) {
         av_log(avctx, AV_LOG_ERROR, "unsupported block align\n");
         return AVERROR_PATCHWELCOME;
     }