Restarting UPower will make every property of UpClient emit a "notify"
signal (as a GDBusProxy would). Avoid mutter reconfiguring the displays
when upower restarts by caching the last known value of "lid-is-closed"
and only reconfiguring the displays if it actually changed.
This fixes a black out of the screen when UPower restarts.
(cherry picked from commit 49b23c749044a855fb3661a0351521f337946c41)
24b87b364d