fix: php warning on PayPal response

[sapayth]

After PayPal payment, when he click to return to the website user are facing critical error in PayPal payment.

[Rubaiyat-E-Mohammad]

Issue-1:
Subscription pack and new transaction are not added

Scenario:

1. From frontend, Log in as a user
2. Try to add subscription pack
3. Complete payment with PayPal
4. Check subscription pack for the user
5. Log out as a user
6. Log in as an admin
7. Go to admin dashboard
8. Click on wp user frontend from side
9. Click on subscription
10. Observe that new subscription is not added
11. Click on transaction
12. Observe that no new transaction happened using Paypal

Screenshot for reference:

Debug-log:

[02-May-2024 11:02:01 UTC] PHP Notice:  Undefined index: subscription.phpyear in /Users/rubaiyatemohammad/QA-Manual-weDevs/SITES/wpuf_rub/wp-content/plugins/wp-user-frontend/includes/Admin/Admin_Subscription.php on line 719

[sapayth]

The issue is related to our subscription pack creation process. we are saving some data in bad format. hopefully this will be resolved in our recent subscription page revamp PR