Don't create duplicate move

supply_on_sale could be changed between two calls on get_move so we must also
check if a purchase request is not yet created.

review857002
(transplanted from b8717ff3e5597d65046fb9da828b56a82d45b512)

sale.py

@@ -82,7 +82,8 @@ class SaleLine:
     def get_move(self, shipment_type):
         move = super(SaleLine, self).get_move(shipment_type)
         if (shipment_type == 'out'
-                and self.supply_on_sale):
+                and (self.supply_on_sale
+                    or self.purchase_request)):
             if self.purchase_request_state in ('', 'requested'):
                 return
         return move