Fix repainting for repaints with small regions

Makes this statement similar to the one that uses pe->rect() instead of pe->region().rects()

You can test it by:
* Opening a document with okular
* Scroll down a bit so that you are not on the top of the viewing area
* Open the review tool
* Move the review tool around
* See how it leaves unrepainted garbage
* See how this patch fixes it
(cherry picked from commit 9f654a0029976965024a09bf3c095f9f07d031cd)