[FIX] website_sale_stock_wishlist: add to cart

Current behaviour:
When activating "Prevent Sale of Zero Priced Product",
zero priced products could still be added to cart,
using the wishlist.

Expected behaviour:
Zero priced products should not be added to cart

Steps to reproduce:
1. Activate the setting "Prevent Sale of Zero Priced Product"
2. Create a product with a sales price of zero
3. Go on the product selling page, cannot be added to cart
4. Add the product to your wishlist
5. Go in the wishlist
6. The product can be added to the cart

Cause of the issue:
add_to_cart_button was overriden

Fix:
Added condition on override

opw-3283057

closes odoo/odoo#121531

Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>