Menu bar should be clipped by the client area of the window and not cover the bottom border

Currently, when a window's height is sufficiently reduced such that only part of the menu bar is drawn, the menu bar covers the bottom border.
However, when you actually click near the bottom edge of the window, you'll discover it still behaves like a border. Hence, it should be drawn as such.
This is probably caused by the menu bar not getting clipped by the window's client area.

Revision: 53070