[FIX] stock: include zero quantity products in search results
[FIX] stock: include zero quantity products in search results

A special case was made for products not available when running a search on
the qty_available field.

For domains like ('qty_available', '<=', 5), it should include non-available
products too.

Fixes #18336

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo