[FIX] point_of_sale: tip value not a discount

When we are adding a tip, the unit_price of the tip product is changed
on the line, but not the lst_price, that lead to show the difference
between the lst_price and unit_price as a discount on the receipt if the
pricelist is configured to show its price difference as a discount.

So we are now also changing the lst_price.

TASK-ID: 2058650

addons/point_of_sale/static/src/js/models.js

@@ -2011,6 +2011,11 @@ exports.Orderline = Backbone.Model.extend({
     get_lst_price: function(){
         return this.product.lst_price;
     },
+    set_lst_price: function(price){
+      this.order.assert_editable();
+      this.product.lst_price = round_di(parseFloat(price) || 0, this.pos.dp['Product Price']);
+      this.trigger('change',this);
+    },
 });
 
 var OrderlineCollection = Backbone.Collection.extend({
@@ -2544,10 +2549,11 @@ exports.Order = Backbone.Model.extend({
             for (var i = 0; i < lines.length; i++) {
                 if (lines[i].get_product() === tip_product) {
                     lines[i].set_unit_price(tip);
+                    lines[i].set_lst_price(tip);
                     return;
                 }
             }
-            this.add_product(tip_product, {quantity: 1, price: tip });
+            this.add_product(tip_product, {quantity: 1, price: tip, lst_price: tip });
         }
     },
     set_pricelist: function (pricelist) {
@@ -2611,6 +2617,10 @@ exports.Order = Backbone.Model.extend({
             line.set_unit_price(options.price);
         }
 
+        if(options.lst_price !== undefined){
+            line.set_lst_price(options.lst_price);
+        }
+
         //To substract from the unit price the included taxes mapped by the fiscal position
         this.fix_tax_included_price(line);