Fix bug when ROI is anything but p1:top-left and p2:bottom-right.
Fix bug when ROI is anything but p1:top-left and p2:bottom-right.

Fix crash when region of interest is selected from any side - like
drawing the ROI from bottom-right to top-left or similar in GUI mode.

This does work in non-GUI mode too.

szanni/slideextract,szanni/slideextract