[FIX] point_of_sale: prevent adding not saleable product with scan

Current behavior:
When scanning the barcode of a product that is not saleable, the product
was added to the order.

Steps to reproduce:
- Create a product that is not saleable and not available in PoS
- Set a barcode for this product
- Open the PoS, and scan the barcode of the product
- The product is added to the order even if it is not saleable

opw-3325238

closes odoo/odoo#124804

Signed-off-by: Joseph Caburnay (jcb) <jcb@odoo.com>