Fix issue where deleted cube would remain on screen if it was the only open cube.
Fix issue where deleted cube would remain on screen if it was the only open cube.

bheekin/n-cube-editor,jdereg/n-cube-editor,jdereg/n-cube-editor,jsnyder4/n-cube-editor,bheekin/n-cube-editor,tympollack/n-cube-editor,jdereg/n-cube-editor,tympollack/n-cube-editor,kpartlow/n-cube-editor,kpartlow/n-cube-editor,jsnyder4/n-cube-editor