Cannot select context menu items that overlap the dock

[dkonigsberg]

Description

When a context menu expands downward, and covers the dock, menu items overlapping the dock area are unselectable.

Its hard to attach a useful screenshot, because none of my screenshot tools capture the mouse pointer.

Steps to reproduce

1. Move an application that has downward-expanding context menus to the bottom of the screen, just above the dock. (HexChat's entry field is a good example of this, as is anything that presents a context menu too long to actually fit on the screen)
2. Right-click in a control that presents such a context menu (i.e. the HexChat entry field)
3. Try to move the mouse up-and-down in the context menu, and observe that only menu items above the dock can actually be selected.