Update invoice.rb: calculate expected_amount also if invoice has no o…

…rders

if an invoice has only deliveries but nor orders, expected amount returned the invoice net-amount but not the deliveries. if an invoice has no orders and deliveries, expected_amount is now 0.

app/models/invoice.rb

@@ -51,8 +51,6 @@ def deliveries_sum(type = :without_markup)
   end
 
   def expected_amount(type = :without_markup)
-    return net_amount unless orders.any?
-
     orders_sum(type) + orders_transport_sum + deliveries_sum(type)
   end