Fix scopeScene's use of Box3F constructor

The `Box3F` constructor accepting a single float [treats it as a diameter, not a radius](https://github.com/GarageGames/Torque3D/blob/d08e594316e69651b6b6c8a07063d9111b2af688/Engine/source/math/mBox.h#L249). Therefore we need to double `visibleDistance` before we pass it in.