Update installer_base.lib.php to attend to comment...

Update installer_base.lib.php to attend to comment ispconfig/ispconfig3!911 (comment 69118). Not sure if this could fix the compatibality for php5.3 which is still supported by current version of ISPConfig but seems that solution is being used in interface/lib/classes/functions.inc.php. This suggestion solution for php5.3 is not tested.