[FIX] website_sale: prevent crash if setting qty to 0 in cart update

When there is an optional product for which the quantity is set to 0 because
there is no stock available, the cart update would raise because it tried to
read the order line even though it was deleted above.

Now we apply the logic only if the order_line actually exists.

Part of task 1950712

closes odoo/odoo#31779

Signed-off-by: Lucas Perais (lpe) <lpe@odoo.com>

addons/website_sale/models/sale_order.py

@@ -280,14 +280,14 @@ class SaleOrder(models.Model):
 
             order_line.write(values)
 
-        # link a product to the sales order
-        if kwargs.get('linked_line_id'):
-            linked_line = SaleOrderLineSudo.browse(kwargs['linked_line_id'])
-            order_line.write({
-                'linked_line_id': linked_line.id,
-                'name': order_line.name + "\n" + _("Option for:") + ' ' + linked_line.product_id.display_name,
-            })
-            linked_line.write({"name": linked_line.name + "\n" + _("Option:") + ' ' + order_line.product_id.display_name})
+            # link a product to the sales order
+            if kwargs.get('linked_line_id'):
+                linked_line = SaleOrderLineSudo.browse(kwargs['linked_line_id'])
+                order_line.write({
+                    'linked_line_id': linked_line.id,
+                    'name': order_line.name + "\n" + _("Option for:") + ' ' + linked_line.product_id.display_name,
+                })
+                linked_line.write({"name": linked_line.name + "\n" + _("Option:") + ' ' + order_line.product_id.display_name})
 
         option_lines = self.order_line.filtered(lambda l: l.linked_line_id.id == order_line.id)
         for option_line_id in option_lines: