bug#44502: 28.0.50; Emacs crash using new frame

[Andy Moreton]

On Sat 07 Nov 2020, Andy Moreton wrote:

> Emacs crashed when using a new frame. After a bootstrap of master, I
> could repeat the crash witht he following recipe:
>   - Run "emacs -Q"
>   - Type "C-x 5 2 RET" to create a new frame (which becomes selected)
>   - Type "C-x C-f" and emacs crashes
>
> I bisected this using the recipe above, with:
>   git checkout master
>   git bisect start
>   git bisect bad
>   git bisect good c3a20804a8
>
> Bisect reports the bad commit as:
>   2ecbf4cfae Allow minibuffer to stay in its original frame.
>              (2020-11-05 Alan Mackenzie)

This emacs was built with --enable-checking, so the crash is actually an
eassert in select_window (in window.c).

    AndyM