[FIX] point_of_sale: prevent scanning on receipt

- Sell a Product A
- From receipt screen, scan the barcode of Product B
- B will be in tab along with A
- Pay and validate
- Close the session

Only an order with Product A is recorded in the session (order 1).

When performing this set of actions, a new order is not created: the POS
simply reuses the current order. However, `create_from_ui` (called in
the receipt screen) discards an order if the reference already exists.
This means that the first order is correctly synchronized at validation,
while the second order is silently discarded.

Closes #16781
opw-766459

addons/point_of_sale/static/src/js/screens.js

@@ -1908,6 +1908,7 @@ var PaymentScreenWidget = ScreenWidget.extend({
         }
 
         order.initialize_validation_date();
+        order.finalized = true;
 
         if (order.is_to_invoice()) {
             var invoiced = this.pos.push_and_invoice_order(order);
@@ -2010,4 +2011,3 @@ return {
 };
 
 });
-