[Deskbar] Auto-raise does not work correctly when covered by a window

[x-ist]

This is hrev44584.

0. Drag the Deskbar to the lower screen edge.
1. Enable Auto-raise.
2. Open a window, e.g. a Tracker window
3. Move the window such that it covers the Deskbar beyond the lower screen edge
4. Hover the mouse down the window to the screen edge carefully without hovering over the Deskbar.
5. Deskbar is NOT raised.

6. Now hover over the Deskbar (not necessarily the edge)
7. Now hover the mouse again down the window to the screen edge carefully without hovering over the Deskbar.
8. This time it's raised.