ZoomSlider: Don't react to rocker keys if we are not visible
ZoomSlider: Don't react to rocker keys if we are not visible

This allows the overlay to opt out of such behavior by hiding the slider

foolab/cameraplus,mer-hybris-kis3/cameraplus,foolab/cameraplus,foolab/cameraplus,mer-hybris-kis3/cameraplus,mer-hybris-kis3/cameraplus,foolab/cameraplus,mer-hybris-kis3/cameraplus