[FIX] product, web: many2one child of value

Before this commit, when a product category had a similar name than an other
e.g. ALL / Exp and ALL / Expenses

When entering the list view of its products, it displayed the product linked to the category with the similar name
e.g. When opening ALL/Exp products list, it displayed its products **plus** the products of ALL/Expenses

After this commit the list view just contains the active category's products

OPW 782905