avformat/wavdec: Check that smv block fits in available space

Fixes: OOM
Fixes: 56271/clusterfuzz-testcase-minimized-ffmpeg_dem_WAV_fuzzer-5290810045497344

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

@@ -730,6 +730,10 @@ smv_retry:
                 goto smv_out;
             }
             size = avio_rl24(s->pb);
+            if (size > wav->smv_block_size) {
+                ret = AVERROR_EOF;
+                goto smv_out;
+            }
             ret  = av_get_packet(s->pb, pkt, size);
             if (ret < 0)
                 goto smv_out;