[FIX] pos_self_order_sale: check if the field really exists

When the module "sale_product_configurator" is not installed, an AttributeError is raised

Steps to reproduce:

Install the "point_of_sale" app, the "pos_self_order_sale" module and remove the "sale_product_configurator" module
Go to settings -> point of sale -> Self ordering: QR Menu -> preview web interface
Cause:
The field "optional_product_ids" is provided by the module "sale_product_configurator" which is not a dependency of this module

opw-3850421

closes odoo/odoo#161921

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

addons/pos_self_order_sale/models/product_product.py

@@ -9,5 +9,8 @@ class ProductProduct(models.Model):
     def _get_product_for_ui(self, pos_config):
         self.ensure_one()
         product = super()._get_product_for_ui(pos_config)
-        product["optional_product_ids"] = self.optional_product_ids.product_variant_ids.ids
+
+        if "optional_product_ids" in self.env["product.product"]:
+            product["optional_product_ids"] = self.optional_product_ids.product_variant_ids.ids
+
         return product