Fix a crash when browsing empty roots.

     * Requests focus on the item that last had focus. Scrolls to that item if necessary.

     */

    public void restoreLastFocus() {

        if (mAdapter.getItemCount() == 0) {

            // Nothing to focus.

            return;

        }

        if (mLastFocusPosition != RecyclerView.NO_POSITION) {

            // The system takes care of situations when a view is no longer on screen, etc,

            focusItem(mLastFocusPosition);