[16.][IMP] purchase_sale_stock_inter_company: sync returns from SO to PO

[AaronHForgeFlow]

Also:

[IMP] purchase_sale_stock_inter_company: do not show error when increasing the quantity in the sale order when the previous picking is already processed

Motivation:

• Returns are not syncing (in any version not only 16)

• Errors when increasing the quantity or process a delivery after a return is made).

• Steps to reproduce:

1. Enable sale order auto confirmation in San Francisco and Chicago
2. When creating the PO in San Francisco, a sale order in Chicago is created
3. When confirming the SO, the delivery gets created. Set the quantities and validate the delivery. The receipt has been validated in San Francisco.
4. Now make a return in the delivery. Return all quantities. No return has been made in San Francisco.
5. Try to deliver again the products (you can do it by updating the quantity of the SO line and then put it back to the original quantity, this creates a delivery).
6. You will get an error: "There's no corresponding line in PO bla bla

On top of #881 to avoid conflicts