[ticket/12570] Fix MySQLi affectedrows by specifying MYSQLI_CLIENT_FOUND_ROWS

PHPBB3-12570
[ticket/12570] Fix MySQL affectedrows

We always want the number of matched rows instead of changed rows,
when running an update. So when mysql_info() returns the number of
matched rows we return that one instead of mysql_affected_rows()

PHPBB3-12570