When a new floating MDI window was created, its position was tracked
from the very beginning. This caused the window's initial move event,
generated by the show() method, to be handled by the undocking
mechanism.

This event might contain outdated position information that, in certain
cases, could trigger immediate re-docking of the floating window,
setting its pointer to 0. If this happened, then the remaining code that
configured the floating window would dereference the null pointer and
crash the application.

To fix the error, connect the floating window's signals only after it
has been fully configured. This way its initial move events are ignored.