Fix restoring columns in certificatedetailsdialog

Waiting for key listing to be done wasn't correct;
The relevant part was that it's executed at a later point in time.
Since, when opening a Certificate details dialog, the KeyCache was already
initialized, this was executed immediately, meaning that restoring the layout didn't work.

(cherry picked from commit c288a7951e3c5071cca333909fe52081c53580b9)