Pull Down Menu placement is broken when Parent is part way off the screen on the right

To reproduce, move a window with a menu, like notepad, so the menu item is nearly off the right of the screen. Then,  click it. The menu won't align with the screen right edge.

Example:

W2K3SP2 works fine:

After Fix:

This happens on the latest version of ReactOS which is 0.4.15-dev-8486-g90de2b6.
Absolutely nothing shows up in the debug log when this happens.
A possible fix is attached here: menu-fix-03.patch
Originally reported by I_Kill_Bugs in CORE-16729.