KeyboardDragListener end listener fired regardless of whether it is currently dragging

[jessegreenberg]

A bug introduced from #1621. If the KeyboardDragListener is not dragging but the Hotkeys indicate it is pressed, the end action will still execute. This is possible if the dragging doesn't start because the Pointer is already attached (interacting with another target already - likely a descendent that got the event first). This should be fixed.

[jessegreenberg]

Fixed in the above commit. This is a similar case to #1634. Just like that issue, this was missed in earlier testing because Hotkey generally handles this. But because AccessibleSlider does not use KeyboardListener (and therefore Hotkey), we hit this case. This change is correct for KeyboardDragListener, but AccessibleSlider should be changed to use KeyboardListener.