gtkapplication-dbus: Fetch inital screen saver state async
Avoid a sync call that can make the application block for no good reason.
I've seen a deadlock between an application using GtkApplication
and the screensaver providing program
since that called back into the application via GetManagedObjects
for a totally unrelated interface and
since GetManagedObjects
is sync in glib too.
This deadlocks until the DBus timeout is hit.
I need to look at the glib too but the GTK it's good to avoid the sync call on the glib side as well.
If that flies i'll add a gtk 3 version.
Fixes 6bfe1710