[th/client-object-manager-dbus-leak]

NMClient's context-busy-watcher does not account for another idle action (that is due to g_dbus_connection_signal_subscribe()'s destroy notify). That can cause GSources attached to the GMainContext at the point when the context-busy-watcher indicates that we are done.

That is especially bad with synchronous initialization, because then we have a inner GMainContext and we un-integrate it too early. That means, the pending source will never be consumed and leaked indefinitely.

Fix that.