Add empty control labels to layout

Empty labels were not added properly and due to that layout went
wrong when there was such controls (control class names).

Signed-off-by: Antti Palosaari <crope@iki.fi>
Write unknown control text when control is not known

Restore a little bit back to earlier functionality and write unknown
control label in some cases.

Signed-off-by: Antti Palosaari <crope@iki.fi>