Don't show action "Create invoice" for stock order

app/views/finance/balancing/new.html.haml

@@ -21,7 +21,7 @@
     %h2 Aktionen
   .column_content
     %ul
-      - unless @order.invoice
+      - unless @order.invoice or @order.stockit?
         %li= link_to "Rechnung anlegen", new_finance_invoice_path(:order_id => @order, :supplier_id => @order.supplier)
       - unless @order.closed?
         %li= link_to "Bestellung abschließen", :action => "confirm", :id => @order