Systems with only one user show the switch user menu nonetheless.

The default behaviour should be:

  * 1 user -> only of "Lock" menu item
  * more than 1 user -> show the lock / switch user menu list

On Lomiri on Debian / Ubuntu vanilla this is not working as expect. Also with just one user per system, the user menu list gets shown.

https://github.com/AyatanaIndicators/ayatana-indicator-session/blob/main/src/service.c#L705