bug#27454: C-S-g [keyboard-quit] doesn't work to get out of disabled command choice

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Sun, 21 Jul 2019 17:48:54 +0200
> Cc: 27454@debbugs.gnu.org
> 
>        (while (progn (setq char (read-event))
>                    (or (not (numberp char))
>                        (not (memq (downcase char)
>                                   '(?! ?y ?n ?\s ?\C-g)))))
>        (ding)
>        (message "Please type y, n, ! or SPC (the space bar): "))))
>  
> 
> 
> Because normally C-S-g works the same as C-g (see below).  Should we
> perhaps just add C-S-g to the events this function checks for?

But C-S-g is not a character.