Cannot access return array in AdminOrdersController.php

As seen in http://php.net/manual/en/language.types.array.php#example-102, is not possible to access the array key of the return of a function directly prior to PHP 5.4.

A temporary variable should be used to solve the problem for previous versions.
Merge pull request #2310 from snamor/patch-1

[-] BO : Cannot access return array in AdminOrdersController.php