Benjamin Berg authored Mar 07, 2019 and Georges Basile Stavracas Neto committed Mar 11, 2019

The dialog tried to retain the current configuration mode. However,
doing so means that we end up in the wrong mode in some situation (e.g.
opening the dialog with two displays but only one enabled).

Fix this by always selecting a configuration mode. This potentially
switches the user from "join" to "single" if only one monitor is left.
However, the user has no way to do this manually, so no unexpected UI
change will happen.