At the edge of the view, a line segment could end up as not producing
any pixels even if not clipped by the floating-point clip
routine. Make sure the starting point for the next line is still
updated correctly for any significant segment lengths.

Change-Id: I381a4efb81ce6006f3da4c67abf279aea79e4663
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>