Warning displays before joining a BuddyBoss group

[michaelbeil]

Describe the bug Warning displays before joining a BuddyBoss group

To Reproduce Steps to reproduce the behavior:

1. Go to a group on the front end
2. See error -

Warning: Undefined array key "link_class" in /wp-content/plugins/pmpro-buddypress/includes/restrictions.php on line 82

Screenshot

Expected behavior There should not be an error.

This came up in ticket (ID 508028) and I could replicate it there with PHP 8.0.26.

WordPress Environment

``` Paid Memberships Pro 2.11.2, BuddyPress & BuddyBoss Add On 1.4.1, BuddyBoss Platform 2.3.81, BuddyBoss Platform Pro 2.3.70, WordPress 6.2.2, PHP 8.0.26 ```

[dwanjuki]

This came up again in ticket 522111.

Replicated on PHP 8.0.30, PMPro 2.12.3, PMPro BuddyPress 1.4.1

[dwanjuki]

Another customer encountered this issue. Mods: 575846