Here are a few improvements regarding the latests changes of /controllers/front/standardreturn.php
The ini_set() at the beginning of the file should be removed.
You should check that external_reference has been defined, with Tools::getIsset('external_reference'), and you should check has been properly loaded with Validate::isLoadedObject($cart)
Here are a few improvements regarding the latests changes of /controllers/front/standardreturn.php
external_referencehas been defined, withTools::getIsset('external_reference'), and you should check has been properly loaded withValidate::isLoadedObject($cart)