bug#47969: 28.0.50; Losing minibuffer focus in trying M-x command

[Gregory Heytings]

> > > I don't know.  What I do know is that mouse-autoselect-window was 
> > > introduced in Emacs 22, and that in Emacs 22-25 the lower window was 
> > > not selected with that recipe.  That behavior changed in Emacs 26.
> >
> > Do you know which commit changed it?
>
> I'll try to find that.

Okay, I bisected this, and the culprit is commit 3fdd3bb56c. 
Interestingly, that commit removed the following from 
handle-select-window:

;; Don't switch if we're currently in the minibuffer.
;; This tries to work around problems where the
;; minibuffer gets unselected unexpectedly, and where
;; you then have to move your mouse all the way down to
;; the minibuffer to select it.
(window-minibuffer-p)

which happens to be what my patch adds again.