more focus / crash fixes: assertion fired due to fast left-direction scrolling in a large grid which would produce getCellNode() requests that would, at least temporarily, reside *outside* the visible area (calls that occur before active cell is moved into view). The getCellNode() 'mandatory' branch code conditions have been simplified to allow node requests outside the visible area like that. Tests show that the scroll performance is the same while no further crashes occur.
kill the commented-out looping inside getCellNode(): that loop was only coded to help debug the crash situation.