keditfiletype: fix crash when adding apps to "empty" views

thou shalt not c-cast => let's dynamic cast, through dynamic cast we'll
notice that the items aren't actually what we thought they should be and
then we can skip them.

notably when there is no app association we insert a fake 'None' entry,
this entry is still present when updatePreferredServices runs but needs
skipping because it does not represent a service

I should note that the UX for the new-association use case is fairly
buggy still, but at least it doesn't crash

BUG: 481229


(cherry picked from commit c099d4b0)