Wait list setting notice when editing registration

If the wait list setting is unchecked (or module is off) and I edit an individual registration when there is no more room I get Notice: Undefined index: registration_waitlist_enable.
The issue happens on line 27 of registration.forms.inc. When the form loads and there is no room left for registrations, it looks for $settings['settings']['registration_waitlist_enable'] however that setting is only added when wait list is checked in the registrations settings.

To fix the issue, there should be a check for the settings: isset($settings['settings']['registration_waitlist_enable'])