added mysqli_connect to mysql sanity check

as mysqli is now fully working i added mysqli_connect to the mysql sanity-check
now tt-rss works even if php_mysql is not activated

the database updater currently seems not work ->

Parse error: syntax error, unexpected '$', expecting variable (T_VARIABLE) in C:\inetpub\wwwroot\tt-rss\classes\dbupdater.php on line 5

Fatal error: Query INSERT INTO ttrss_error_log (errno, errstr, filename, lineno, context, owner_uid, created_at) VALUES (256, 'Query INSERT INTO ttrss_error_log\n (errno, errstr, filename, lineno, context, owner_uid, created_at) VALUES\n (4, \'syntax error, unexpected \\\'$\\\', expecting variable (T_VARIABLE)\', \'classes\\\\dbupdater.php\', \'5\', \'\', 1, NOW()) failed: Table \'tt-rss.ttrss_error_log\' doesn\'t exist', 'classes\\db\\mysqli.php', '27', '', 1, NOW()) failed: Table 'tt-rss.ttrss_error_log' doesn't exist in C:\inetpub\wwwroot\tt-rss\classes\db\mysqli.php on line 27