Description of the Change

This PR fixes an issue where a warning is thrown when protected content is enabled and WP_Query runs in the AJAX callback

Closes #4059

How to test the Change

1. Enable the protected content feature.
2. Add add_filter( 'ep_ajax_wp_query_integration', '__return_true' ); filter
3. Call the WP_Query with a search parameter and ensure the orderby parameter is empty in the ajax callback function

Changelog Entry

Fixed - Attempt to read property "base" on null

Credits

Props @burhandodhy @yarovikov

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added Critical Flows, Test Cases, and/or End-to-End Tests to cover my change.
• All new and existing tests pass.