Bug fix #35307

Popup menus in nodes, with nodes outside window boundary, were clipped very badly, even
causing it to fill entire window.

Now the clip code nicely translates the menu horizontally to be in view.



git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56688 954f8c5b-7b00-dc11-b283-0030488c597c