fix: prevent fatal error when refreshing licenses

[ravinderk]

Bug Report

User Story

As an admin, I want to update the license without any issue.

Current Behavior

Admin will get a fatal error if he is on WP <= 4.9.10

PHP Fatal error: Uncaught Error: Cannot use object of type stdClass as array in /wp-includes/class-wp-list-util.php:150
Stack trace:
#0 /wp-includes/functions.php(3697): WP_List_Util->pluck('check_license', NULL)
#1 /wp-content/plugins/give/includes/misc-functions.php(2410): wp_list_pluck(Object(stdClass), 'check_license')

related ticket:
https://secure.helpscout.net/conversation/902058350/43406/
https://secure.helpscout.net/conversation/902220799/43422?folderId=672194
https://secure.helpscout.net/conversation/902155992/43413?folderId=672194

Steps to Reproduce

1. Install WP 4.9.10
2. Add add-on license (maybe you will also get a fatal error when adding license)
3. Open license setting page

Acceptance Criteria

• I am not getting PHP fatal error when refresh license on WP <=4.9.10 or WP>4.9.10.

[mathetos]

I'm not sure but this ticket seems to suggest this error also happens on WP version 5.0.2
https://secure.helpscout.net/conversation/904914308/43578/

[DevinWalker]

@mathetos yes it occurs on that version as well. I've confirmed this resolves the underlying issue though.