Tour Macro: Render Defaults if Page is not (yet) found

If the Tour Macro references pages that have not (yet) been stored (the view may be rendered while the referenced pages have not been generated on the save hook), the rendering should not present an error message, but render the references as titles.

Hopefully this enhances the user experience. Alternatives would be a warning that signals to reload the page or render nothing at all (what may be puzzling for the user).