bug#63655: 29.0.91; Dialog box not displayed upon closing frame

[Eli Zaretskii]

> Date: Tue, 23 May 2023 13:12:38 +0800
> From:  Po Lu via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> Start Emacs, then set confirm-kill-emacs to t.
> Close the last frame on the only terminal by clicking the close button
> on the WM frame window.  Emacs will ask:
> 
>   Really exit Emacs? (y or n)

confirm-kill-emacs, if non-nil, should be a function.  If I try what
you described above, Emacs signals an error when I close the last
frame.