Panel highlighting when under drawer

[austin-ek]

What happens: When dragging a block over a drawer with a panel under it, the panel gets highlighted even though the drop point is the drawer.

This should only highlight if the panel is the one accepting the block.

Steps to reproduce:

1. Shrink the window so the panel area scrolls sideways.
2. Adjust the panel area so a panel is under the drawer.
3. Drag a block over the drawer
4. Observe that the panel gets highlighted.
5. Drop the block. It will go into the drawer, not the panel