Fix collision display benchmark gui

In benchmark GUI, when you move a goal pose marker around, the end-effector meshes in the middle are supposed to change color to yellow when they are in collision with something and back to normal when they are not.  Prior to this change, that collision detection did not work at all if the end-effector did not have any active joints.  Because of the collision-checking function it was using, it only checked collisions for links downstream from active joints in the given group.  So if it was the PR2 hand, it would have worked to check collisions with the fingers, but not with the palm.  With a fixed tool, it never showed any collisions.