avformat/wavdec: More complete size check in find_guid()

Fixes: signed integer overflow: 9223372036854775807 + 8 cannot be represented in type 'long'
Fixes: 27341/clusterfuzz-testcase-minimized-ffmpeg_dem_W64_fuzzer-5442833206738944

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

@@ -666,7 +666,7 @@ static int64_t find_guid(AVIOContext *pb, const uint8_t guid1[16])
     while (!avio_feof(pb)) {
         avio_read(pb, guid, 16);
         size = avio_rl64(pb);
-        if (size <= 24)
+        if (size <= 24 || size > INT64_MAX - 8)
             return AVERROR_INVALIDDATA;
         if (!memcmp(guid, guid1, 16))
             return size;