bug#59007: rmail-forward generates wrong-type-argument error

[Eli Zaretskii]

> From: Nicolas Graner <nicolas@graner.name>
> Date: Thu, 03 Nov 2022 22:49:43 +0100
> 
> In Emacs 29.0.50 master, the command rmail-forward always generates an
> error.
> 
> To reproduce, open any Rmail file with rmail and type "f".
> 
> Debugger entered--Lisp error: (wrong-type-argument stringp nil)
>   string-match("\\`[^ @]+@[^ @]+\\'" nil nil t)
>   message-mail(nil "[nicolas@graner.name: testing]" ((In-Reply-To) ("cc")) 
> nil nil (rmail-yank-current-message #<buffer bug-test>) ((rmail-mark-message 
> #<buffer bug-test> (1) 5)) (rmail-mail-return #<buffer bug-test>))
>   compose-mail(nil "[nicolas@graner.name: testing]" ((In-Reply-To) ("cc")) 
> nil nil (rmail-yank-current-message #<buffer bug-test>) ((rmail-mark-message 
> #<buffer bug-test> (1) 5)) (rmail-mail-return #<buffer bug-test>))
>   rmail-start-mail(nil nil "[nicolas@graner.name: testing]" nil nil #<buffer 
> bug-test> ((rmail-mark-message #<buffer bug-test> (1) 5)) t)
>   rmail-forward(nil)
>   funcall-interactively(rmail-forward nil)
>   call-interactively(rmail-forward nil nil)
>   command-execute(rmail-forward)
> 
> Explanation:
> 
> In message-mail, code was added to fix incorrect In-Reply-To headers
> sent by Firefox. This code assumes that the value of the header is a
> string, but in messages generated by rmail-forward, the value of
> In-Reply-To is nil.
> 
> Suggested patch:

Thanks, installed.