[ATLAS] Allow returning to current selection to place objects

[historic_bruno]

Normally, when you select from Atlas' object list, you will activate the placement tool. However, this only seems to work when you change the last selection. If you choose a different tool (maybe to select and delete things), you can't return directly to placing the last object. Instead you must select a different object, then go back to the one you wanted. It's even more annoying if you have filtered the choices down to one, because then there's no way of reactivating placement without first removing the filter.

[trompetin17]

another way to fix this ​https://code.wildfiregames.com/D2040