Fix/paginate links warning

[ideadude]

Description

A user reported this issue in the 7.7 update on wp .org here: https://wordpress.org/support/topic/preg_replace-passing-null-to-parameter-3-subject/#post-17939000

Our code like echo wp_kses_post( paginate_links( ... ) ); would sometimes return warnings if the results of the paginate_links call was empty. This is because wp_kses_post called wp_kses, which calls preg_replace at some point down the line, which expects the content being replaced is not empty.

We now set a variable using paginate_links, then check if that result is non empty before echoing and calling wp_kses_post.

How has this been tested?

Manually loading the memberships and notifications pages of the student dashboard with both pagination and not.

Checklist:

• This PR requires and contains at least one changelog file.
• My code has been tested.
• My code passes all existing automated tests.
• My code follows the LifterLMS Coding & Documentation Standards.