bug#59206: rmail-summary-apply-filters-consecutively causes wrong-type-argument error

[Eli Zaretskii <eliz@gnu.org>]

> From: Nicolas Graner <nicolas@graner.name>
> Date: Fri, 11 Nov 2022 23:49:22 +0100
> 
> When the variable rmail-summary-apply-filters-consecutively is non-nil,
> if you execute one of the rmail-summary-by-* commands when there is no
> existing summary, you get an error.
> 
> This is because those commands call
> rmail-summary-fill-displayed-messages, which assumes
> rmail-summary-buffer is a buffer, but in this case it is nil.
> 
> Example (starting from emacs -Q):
> 
> C-u M-x rmail [any rmail file]
> M-: (setq rmail-summary-apply-filters-consecutively t)<RET>
> M-x rmail-summary-from-senders<RET>testing<RET>
> 
> Debugger entered--Lisp error: (wrong-type-argument stringp nil)
>   rmail-summary-fill-displayed-messages()
>   rmail-summary-by-senders("testing")
>   funcall-interactively(rmail-summary-by-senders "testing")
>   call-interactively(rmail-summary-by-senders record nil)
>   command-execute(rmail-summary-by-senders record)
>   execute-extended-command(nil "rmail-summary-by-senders" "rmail-summary-by-senders")
>   funcall-interactively(execute-extended-command nil "rmail-summary-by-senders" "rmail-summary-by-senders")
>   call-interactively(execute-extended-command nil nil)
>   command-execute(execute-extended-command)

Thanks.

This part of Rmail is currently being worked on, and there's an
uninstalled patch in the queue.  If that patch doesn't fix this
problem, I'm sure Andrea (CC'ed) will do that as part of the updated
patch, when we finish discussions of his last patch.