Warning in AdminController.php

If debugging is on (_PS_MODE_DEV_ set to TRUE)
On a fresh install there is a warning on line 1542 in
/classes/controller/AdminController.php in function
addToolBarModulesListButton().
Because of the warning xml files are not populated with data.

Warning: simplexml_load_file()
1: parser error : Document is empty
Merge pull request #690 from Ha99y/20130903_addToolBarModulesListButton

[-] BO : Remove warning in AdminController.php