[FIX] sale: correct translation of sale description in shopping cart

Current behaviour:
In the eCommerce, if you add a product that has a sale description
(properly translated) in a website that is set in another language
than the default for the company, the description of the product in
the shopping cart was the default for the company, not the one set
on the website.

Expected behaviour:
Product description language should follow the website's language,
in both the eCommerce, and in the shopping cart.

Steps to reproduce:
- Install eCommerce
- Add a second language of choice and add it to the website
- On a product add a sale's description in both languages
- Logout, go on the e-shop on your product, switch the website to
  language 2
- Observe that the language of the description is indeed language 2
- Add it to cart, go in the cart.
- Observe that the language of the description is language 1, not 2.

Reason for the problem:
Since the cart is a `sales.order`, and each item in it is a
`sale.order.line`, we use the language of the partner for the
description. But by default the language of the public user is the
same as the company, not the one from the current context, which
would be the one from the website.

Fix:
We don't take the language of the partner, if that partner is the
`public user`.

Affected versions:
- saas-15.2
- 16.0
- saas-16.1
- master

opw-3142666

closes odoo/odoo#112738

X-original-commit: 2b0c52e08c35607c9ad75b491978231037a1340c
Signed-off-by: William Braeckman (wbr) <wbr@odoo.com>
Signed-off-by: Piryns Victor (pivi) <pivi@odoo.com>

addons/sale/models/sale_order_line.py

@@ -299,8 +299,9 @@ class SaleOrderLine(models.Model):
         for line in self:
             if not line.product_id:
                 continue
-
-            name = line.with_context(lang=line.order_partner_id.lang)._get_sale_order_line_multiline_description_sale()
+            if not line.order_partner_id.is_public:
+                line = line.with_context(lang=line.order_partner_id.lang)
+            name = line._get_sale_order_line_multiline_description_sale()
             if line.is_downpayment and not line.display_type:
                 context = {'lang': line.order_partner_id.lang}
                 dp_state = line._get_downpayment_state()