[FIX] loyalty: prevent trace back when user deleted ewallet_product_50 record

This error was caught by sentry.

Steps to produce:-

* Install eCommerce,loyalty module.
* Delete 'Top-up eWallet' product from eCommerce/product.
* Then  create a new Gift card & eWallets from eCommerce/Gift card & eWallets.
* At this moment A trace back raise.

Because user deleted the product 'Top-up eWallet'.

Sentry:-3985154178

closes odoo/odoo#116738

X-original-commit: e5ae091a530de45741749e01d25f436af093a8a2
Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>

addons/loyalty/models/loyalty_program.py

@@ -253,7 +253,7 @@ class LoyaltyProgram(models.Model):
                 'rule_ids': [(5, 0, 0), (0, 0, {
                     'reward_point_amount': '1',
                     'reward_point_mode': 'money',
-                    'product_ids': self.env.ref('loyalty.ewallet_product_50'),
+                    'product_ids': self.env.ref('loyalty.ewallet_product_50', raise_if_not_found=False),
                 })],
                 'reward_ids': [(5, 0, 0), (0, 0, {
                     'reward_type': 'discount',