Fix scroll/resize handle missing behavior.
Fix scroll/resize handle missing behavior.

SylvainCorlay/ipywidgets,SylvainCorlay/ipywidgets,jupyter-widgets/ipywidgets,jupyter-widgets/ipywidgets,SylvainCorlay/ipywidgets,ipython/ipywidgets,ipython/ipywidgets,cornhundred/ipywidgets,ipython/ipywidgets,cornhundred/ipywidgets,SylvainCorlay/ipywidgets,jupyter-widgets/ipywidgets,cornhundred/ipywidgets,cornhundred/ipywidgets,cornhundred/ipywidgets,ipython/ipywidgets,ipython/ipywidgets,jupyter-widgets/ipywidgets