status/system: Fix session submenu visibility
Commit 147a743d moved the suspend and power-off actions into the submenu that contains the log-out and switch-user actions, but did not update the submenu visibility logic to account for the additional actions.
As a result, the submenu is hidden when log-out and switch-user are unavailable (like on the login screen), even if suspend and power-off are enabled.
Fixes #2169 (closed)