Especially when GC is enabled, a valid item of `module->types` needs additional
checks before casting to WASMFuncType.
Also, avoid overflowing if reftype_map_count is 0.
Additionally, correctly set IN_OSS_FUZZ based on CFLAGS_ENV for sanitizer
configuration. Update ASan and UBSan messages for clarity in non-oss-fuzz
environments.
