[MlMt] layout bug

[Erik Mueller-Harder]

> Hmm, seems to work for me. Did you relaunch more than once? The fix 
> requires that the test version is also used when quitting with a 
> hidden mailbox outline.

I thought it might: so, yes, I did.

> If yes, then which layout are you using?

Widescreen.  (Can’t bear it myself; I use three-pane with the 
mailboxes *showing*, but my wife likes Widescreen with no boxes showing. 
  Nice to have alternatives!)

— Erik