master 7e8d1b0: Avoid errors in rmailsum for messages without "From"

[Eli Zaretskii]

branch: master
commit 7e8d1b08e3e23bc783cad10e620c2ebe6536965c
Author: Nick Gasson <nick@nickg.me.uk>
Commit: Eli Zaretskii <eliz@gnu.org>

    Avoid errors in rmailsum for messages without "From"
    
    * lisp/mail/rmailsum.el (rmail-header-summary): Be defensive about
    the presence of the "From" header.  (Bug#49770)
    
    Copyright-paperwork-exempt: yes
---
 lisp/mail/rmailsum.el | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lisp/mail/rmailsum.el b/lisp/mail/rmailsum.el
index 44cff21..ac933b9 100644
--- a/lisp/mail/rmailsum.el
+++ b/lisp/mail/rmailsum.el
@@ -758,7 +758,8 @@ the message being processed."
                    len mch lo newline)
                ;; If there are multiple lines in FROM,
                ;; discard up to the last newline in it.
-               (while (setq newline (string-match "\n" from))
+               (while (and (stringp from)
+                           (setq newline (string-match "\n" from)))
                  (setq from (substring from (1+ newline))))
               (if (or (null from)
                       (string-match