Duke3D: Clipping problem that prevents progression in Duke Hard

The last map of Duke Hard requires you to crouch under a wall-aligned sprite of wires in order to hit a switch.

Unfortunately, as of r7428 (d060ca95) it is no longer possible to do so, thus rendering the map impossible to complete without cheats.

The attached map has the section in question. Prior to r7428, it was possible to move under these sprites.