_ShowEnds dialog flicker

The _ShowEnds dialog flickers on resize.
In reality it flickers more, the frame rate makes it look smoother.

The dialog is not in dark style.
The edges are tricky to grab for resizing, one has to set the mouse pixel perfect.
We can make the window smaller than its content (in V7 we can’t).

The above is the same for other similar dialogs, e.g. Zebra.