[-] Class: When no warehouse configurated set 0 instead of seting ''

In some case during creating PrestaShop order it possible get error "Property OrderDetail->id_warehouse is empty". This happens due not active advanced stock management and as result not correct id_warehouse set. 
For example response from method $this->context->cart->getPackageList()

array(1) {
  [192]=>
  array(1) {
    [0]=>
    array(4) {
      ["product_list"]=>
      array(1) {
        [0]=>
        array(60) {
   ...... SKIP.........
        }
      }
      ["carrier_list"]=>
      array(1) {
        [0]=>
        int(0)
      }
      ["warehouse_list"]=>
      array(1) {
        [0]=>
        NULL
      }
      ["id_warehouse"]=>
      string(0) ""
    }
  }
}

As you see there "id_warehouse" have empty value that failed during validation. 
After apply this patch response will look like:
array(1) {
  [192]=>
  array(1) {
    [0]=>
    array(4) {
      ["product_list"]=>
      array(1) {
        [0]=>
        array(60) {
   ...... SKIP.........
        }
      }
      ["carrier_list"]=>
      array(1) {
        [0]=>
        int(0)
      }
      ["warehouse_list"]=>
      array(1) {
        [0]=>
        NULL
      }
      ["id_warehouse"]=>
      int(0)
    }
  }
}