avformat/wavdec: Check smv_block_size

Fixes: Timeout
Fixes: 39554/clusterfuzz-testcase-minimized-ffmpeg_dem_WAV_fuzzer-4915221701984256

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

libavformat/wavdec.c

@@ -498,6 +498,8 @@ static int wav_read_header(AVFormatContext *s)
             wav->smv_data_ofs = avio_tell(pb) + (size - 5) * 3;
             avio_rl24(pb);
             wav->smv_block_size = avio_rl24(pb);
+            if (!wav->smv_block_size)
+                return AVERROR_INVALIDDATA;
             avpriv_set_pts_info(vst, 32, 1, avio_rl24(pb));
             vst->duration = avio_rl24(pb);
             avio_rl24(pb);