Slides only a single row with a too wide content, when making the cursor movements beyond screen limits.
Works fine when moving both right and left along a too wide row.
Algorithm:
if current row is the cursor's textRow
	if cursor's getToowideRow != cursor's texRow
		reset left edge to 0 (not yet fixed)
	endif
	if cursor is not visible with current LeftEdge
		increase or decrease leftedge so that the cursor is visible
	endif
	add cursor's leftedge to inc_x
endif