Missing base-template

Broken URL: https://engine.surfconext.nl/authentication/idp/help-discover
 throws a generic exception because the template is missing in the base-theme. It only exists in the openconext-theme.

Used here: https://github.com/OpenConext/OpenConext-engineblock/blob/6.13.0/src/OpenConext/EngineBlockBundle/Controller/WayfController.php#L76