Comment 2 for bug 1302852

the code doesn't really assume that the Unity prompt is available

" if ((prompt == PROMPT_NONE) && p && p->end_session_dialog)
        {
          GDBusProxy * proxy = G_DBUS_PROXY (p->end_session_dialog);
          char * name = g_dbus_proxy_get_name_owner (proxy);
          if (name != NULL)
            prompt = PROMPT_WITH_UNITY;
          g_free (name);
        }

      /* can we use zenity? */
      if ((prompt == PROMPT_NONE) && p && p->zenity)
        prompt = PROMPT_WITH_ZENITY;"

name should be null if unity is not active (is not on the bus) and it should hit the second case and go with zenity...