libtracker-control: Avoid g_critical() when unable to connect to bus
I was getting this error when running inside a container that had no D-Bus session bus:
# /opt/tracker/bin/tracker daemon status
(tracker daemon:194): GLib-GObject-CRITICAL **: 15:41:34.247: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Could not get status, manager could not be created, Cannot autolaunch D-Bus without X11 $DISPLAY
This change prevents the g_critical() warning from appearing.