No buildings error message does appear

[FlorianK13]

When users start a simulation for a coordinates pair, where there is no building in our data, the error adress is not shown anymore.

[FlorianK13]

I guess this was introduced in #538

[FlorianK13]

In this line in the merge, the handling of the closest building was deleted. How should we handle this? Reintroduce it?

Maybe by implementing the proposed solution from #394?