[FIX] website_sale: Wrong price_unit in the cart

Steps to reproduce the bug:
- Let's consider two companies C1 and C2
- Let's consider website W
- Activate multi-company
- Disable common contact book and common catalog
- Switch the superuser in company C2
- Activate pricelist
- Create a public pricelist PL for C1 and available on W
- Set up a pricelist with compute price = formula and  based on = cost
- Go Sales > Configuration > tick Multiple Sales Prices per Product and tick Prices computed from formulas
- Create a portal user PU and set PL on him
- Create a product P with cost = 10$ and publish it on W
- Set up the product valuation as: automated
- Log as PU and go on the shop
- Put P on your cart

Bug:

The price of P was 0$ instead of 10$

opw:2092695

closes odoo/odoo#40981

X-original-commit: 40d3fa50
Signed-off-by: Simon Goffin (sig) <sig@openerp.com>