Crash occurs in usertypes.py / Question class due to Python slots
being called on deleted Qt objects. This causes either a TypeError or
an AttributeError (probably depending on the state of the deleted Qt
object?).
Fixed by declaring slots in the Question object explicitly via
decorator "@pyqtSlot()".
Possible further TODOs:
- Find out whether this is a problem for slots in other objects as
well.
- Create unittest for this bug (might me somewhat tricky, though).
34c9a73e32