fix call to log method

plugins/auth_ldap/init.php

@@ -343,7 +343,7 @@ function authenticate($login, $password) {
                 $this->_log('Multiple DNs found for username ' . (string) $login, E_USER_WARNING);
                 return FALSE;
             } elseif ($count === 0) {
-                $this->_log((string) $login, 'Unknown User', E_USER_NOTICE);
+                $this->_log('Unknown User ' . (string) $login, E_USER_NOTICE);
                 return FALSE;
             }