[FIX] point_of_sale: POS anglo-saxon in FIFO

In FIFO, the stock move cost related to the picking of the POS
Order must be used to compute the price.

Fine tuning of this commit: a36ff26

opw:1829801

addons/point_of_sale/models/pos_order.py

@@ -413,14 +413,14 @@ def insert_data(data_type, values):
         return True
 
     def _get_pos_anglo_saxon_price_unit(self, product, partner_id, quantity):
-        # In the SO part, the entries will be inverted by function compute_invoice_totals
-        price_unit = - product._get_anglo_saxon_price_unit()
+        price_unit = product._get_anglo_saxon_price_unit()
         if product._get_invoice_policy() == "delivery":
             moves = self.filtered(lambda o: o.partner_id.id == partner_id).mapped('picking_id.move_lines').filtered(lambda m: m.product_id.id == product.id)
             moves.sorted(lambda x: x.date)
-            average_price_unit = product._compute_average_price(quantity, quantity, moves)
+            average_price_unit = product._compute_average_price(0, quantity, moves)
             price_unit = average_price_unit or price_unit
-        return price_unit
+        # In the SO part, the entries will be inverted by function compute_invoice_totals
+        return - price_unit
 
     def _reconcile_payments(self):
         for order in self: