[Flow] Get an 404 error after switching to "production"-context

[Mira Frei]

I added this to Packages/Libraries/phpoffice/phpexcel/Classes/PHPExcel/Autoloader.php:
if (class_exists("PHPExcel_Autoloader")) return;

But the same error.. the return is without any effect, because php is parsing this file in any case. After parsing (and declaring classes) php is running the code logical. right?