VncDisplay shows horizontal and vertical lines when scaling of the widget is performed for HiDPI display:
This can be avoided by moving the updated rectangle by -0.5 in both directions and increasing its size by 1 in both directions.
Also the values which currently avoid artifacts on non-HiDPI displays has to be modified for both cases when scaling of VNC display is enabled and disabled.
This fixes the issue for 200%, 300% and 400% HiDPI scales.