Cache Size query is null on e.g. MySQL 8 CloudLinux

[PhilMakower]

https://github.com/lesterchan/wp-serverinfo/blob/0484787b31912767d8a2f721db897647dda41b49/wp-serverinfo.php#L493

Generates a WARNING when trying to access the member Value on null

return $query_cache_size_query ? $query_cache_size_query->Value : 0; // var may be NULL