[FIX] website_quote: negative discounts are always included in the display price

Before this commit, negative discounts (surcharges) were shown in the
sales order when the price list have the option : "Show public price &
discount to the customer".

Now,  the negative discounts are included in the display price. This
issue was already been addressed in the sales module (see https://github.com/odoo/odoo/blob/ac170e8a8238a9b0aa468f83b11aabc4cd9493de/addons/sale/models/sale.py#L1046

)

Fine-tunning of : cae506f0

opw-2039071

closes odoo/odoo#35065

Signed-off-by: Jorge Pinna Puissant (jpp) <jpp@odoo.com>