Make it possible to process purchase return orders for warehouses that are externally managed.

Currently, when you create a purchase return order for a warehouse that is externally managed by a WOM warehouse in another legal entity, an inbound shipment order with a negative quantity is created in the WOM legal entity upon release to warehouse of the purchase return order. Nevertheless, one cannot process this inbound shipment order line with a negative quantity in any way (not via WMS scanner app, nor via the client). No work around currently exists in the standard product to cover the process of returning items to a vendor when shipping from a warehouse that is externally managed.