Improve site card if building & room info are missing

The following discussion from !256 (merged) should be addressed:

• @marc.hanisch started a discussion: (+1 comment)

  When neither building nor room have values, this line outputs a single dash, which looks different from the orDefault long dash. Even when it makes this line more complex, we should check if building or room are empty and should use the orDefault helper in the case that both are empty.