fix: error after PayPal payment

[sapayth]

After doing a payment with PayPal, there is an error upon returning back to the website.

fix #1429

[Rat01047]

Issue-1:
PayPal successful transaction is not showing in Transactions page

Steps:

1. Go to frontend > Submit post
2. Complete Payment > Using PayPal
3. Check Back-end > Transaction page > No entry

Screenshot for reference:
http://tinyurl.com/yljdjklx

[Rat01047]

Issue-2:
PayPal successful payment - redirect back to site is not working ---> my Site is http but it is redirecting to https site --> When I update the Url I get notices in frontend

Steps:

1. Go to frontend > Submit post
2. Complete Payment > Enter credentials
3. Payment done > Click Return to Merchant > Link Broken
4. Update Link > Warning notices in frontend

Debug-log:

[31-Jan-2024 04:53:58 UTC] PHP Notice:  Undefined index: custom in /Users/nurul.ratul/QA-Manual/SITES/WPUF_Rat/wp-content/plugins/wp-user-frontend/Lib/Gateway/Paypal.php on line 348
[31-Jan-2024 04:53:58 UTC] PHP Notice:  Undefined index: custom in /Users/nurul.ratul/QA-Manual/SITES/WPUF_Rat/wp-content/plugins/wp-user-frontend/Lib/Gateway/Paypal.php on line 349
[31-Jan-2024 04:53:58 UTC] PHP Notice:  Undefined index: mc_gross in /Users/nurul.ratul/QA-Manual/SITES/WPUF_Rat/wp-content/plugins/wp-user-frontend/Lib/Gateway/Paypal.php on line 351
[31-Jan-2024 04:53:58 UTC] PHP Notice:  Trying to get property 'type' of non-object in /Users/nurul.ratul/QA-Manual/SITES/WPUF_Rat/wp-content/plugins/wp-user-frontend/Lib/Gateway/Paypal.php on line 353
[31-Jan-2024 04:53:58 UTC] PHP Notice:  Trying to get property 'type' of non-object in /Users/nurul.ratul/QA-Manual/SITES/WPUF_Rat/wp-content/plugins/wp-user-frontend/Lib/Gateway/Paypal.php on line 354
[31-Jan-2024 04:53:58 UTC] PHP Notice:  Trying to get property 'user_id' of non-object in /Users/nurul.ratul/QA-Manual/SITES/WPUF_Rat/wp-content/plugins/wp-user-frontend/Lib/Gateway/Paypal.php on line 437
[31-Jan-2024 04:53:58 UTC] PHP Notice:  Undefined index: payment_status in /Users/nurul.ratul/QA-Manual/SITES/WPUF_Rat/wp-content/plugins/wp-user-frontend/Lib/Gateway/Paypal.php on line 438
[31-Jan-2024 04:53:58 UTC] PHP Notice:  Undefined index: mc_gross in /Users/nurul.ratul/QA-Manual/SITES/WPUF_Rat/wp-content/plugins/wp-user-frontend/Lib/Gateway/Paypal.php on line 439
[31-Jan-2024 04:53:58 UTC] PHP Notice:  Trying to get property 'tax' of non-object in /Users/nurul.ratul/QA-Manual/SITES/WPUF_Rat/wp-content/plugins/wp-user-frontend/Lib/Gateway/Paypal.php on line 440
[31-Jan-2024 04:53:58 UTC] PHP Notice:  Trying to get property 'subtotal' of non-object in /Users/nurul.ratul/QA-Manual/SITES/WPUF_Rat/wp-content/plugins/wp-user-frontend/Lib/Gateway/Paypal.php on line 441
[31-Jan-2024 04:53:58 UTC] PHP Notice:  Undefined index: first_name in /Users/nurul.ratul/QA-Manual/SITES/WPUF_Rat/wp-content/plugins/wp-user-frontend/Lib/Gateway/Paypal.php on line 444
[31-Jan-2024 04:53:58 UTC] PHP Notice:  Undefined index: last_name in /Users/nurul.ratul/QA-Manual/SITES/WPUF_Rat/wp-content/plugins/wp-user-frontend/Lib/Gateway/Paypal.php on line 445
[31-Jan-2024 04:53:58 UTC] PHP Notice:  Undefined index: payer_email in /Users/nurul.ratul/QA-Manual/SITES/WPUF_Rat/wp-content/plugins/wp-user-frontend/Lib/Gateway/Paypal.php on line 446
[31-Jan-2024 04:53:58 UTC] PHP Notice:  Trying to get property 'user_id' of non-object in /Users/nurul.ratul/QA-Manual/SITES/WPUF_Rat/wp-content/plugins/wp-user-frontend/Lib/Gateway/Paypal.php on line 471
[31-Jan-2024 04:53:58 UTC] PHP Notice:  Trying to get property 'user_id' of non-object in /Users/nurul.ratul/QA-Manual/SITES/WPUF_Rat/wp-content/plugins/wp-user-frontend/Lib/Gateway/Paypal.php on line 472