"Display unconnected" does not honor selected layers

[dreng]

To reproduce this bug:

• Under "Select Layers", uncheck a layer that contains one or nore unconnected devices
• Notice that your unconnected devices that belong to the unchecked layer disappeared
• Press "Hide Unconnected"
• Press "Display Unconnected" -> Previously disappeared devices reappear. In order to hide them again, you need to check and uncheck the previously unchecked layer again