Similar to CONTRIB-3843, the settings tree is always generated at present, regardless of whether it is required. Additionally, MOODLE_INTERNAL should be checked for.

To fix, wrap the whole lot (including the require_once() calls) in:

defined('MOODLE_INTERNAL') || die;

if ($ADMIN->fulltree) {

    // Existing code

}

This should further reduce page load times as the settings tree won't be generated on every page load - they'll only be generated when in the Activity modules settings tree.