[FIX] website_sale: fix traceback on login page

auth="none" pages don't have self.env.user filled in, this throws a
traceback if you try to get the current cart.
This causes an issue when we try to fetch the cart quantity on the login
page.

closes odoo/odoo#102010

X-original-commit: d1c053158f1d306df1f5f1e9d4c81ee642a73f48
Signed-off-by: William Braeckman (wbr) <wbr@odoo.com>

addons/website_sale/models/website.py

@@ -311,7 +311,7 @@ class Website(models.Model):
 
         if sale_order_id:
             sale_order_sudo = SaleOrder.browse(sale_order_id).exists()
-        elif not self.env.user._is_public():
+        elif self.env.user and not self.env.user._is_public():
             sale_order_sudo = self.env.user.partner_id.last_website_so_id
             if sale_order_sudo:
                 available_pricelists = self.get_pricelist_available()