Fix third person zoom stickiness

Fixes a problem in third person zoom where the camera position sticks upon reaching the boundary radii. @BrettASwift 
How often does this occur? Just reading it, it seems that if the camera is at its max distance and it immediately switched to its minimum distance, this would return since the distance from the rover is less than the distance from the current camera position to the new one. This seems like it would be a valid movement.