[-] CORE : static cache bugfix on getCustomer()

This is **really a bad idea** to use a static variable here, because if you manipulate 2 order instance, and ask for the customer, the second will give you the first's customer...


ex :
$o1 = new Order(1);
var_dump($o1->getCustomer());

$o2 = new Order(2);
var_dump($o2->getCustomer());  // return $o1 customer...