displays: Always enable first output
It doesn't seem to make much sense to activate no output, when all have been disconnected, and one is reconnected. The "do nothing when a display is connected" option should probably have an exception in this case in general.
In the case of X11, this remedies yet another instance of xrandr disconnecting an output when it goes to sleep: when there is only one output and no default profile has yet been defined (in the case of a new installation).
Fixes: #567 (closed)