[2.0.20-3] Underground belts don't behave properly with smart building

[ab20205754]

Attached video describes it all. Undergrounds don't ghost properly over other undergrounds, and they don't build properly when building over ghosts. They also don't add undergrounds when building over an orphaned one like in the last example, but I think that's been in the game for some time now if I'm not mistaken.

[Loewchen]

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