emacs-28 2a4de5e: Fix Subject when forwarding message with 2-line From

[Mike Kupfer]

branch: emacs-28
commit 2a4de5e5e5c3bb1d1022baf2b9a6f8b2acab4aa1
Author: Mike Kupfer <mkupfer@alum.berkeley.edu>
Commit: Mike Kupfer <mkupfer@alum.berkeley.edu>

    Fix Subject when forwarding message with 2-line From
    
    * lisp/mh-e/mh-comp.el (mh-forwarded-letter-subject): Collapse
    two-line From headers into a single line (SF#266).  Based on a
    suggestion from Lester Buck (many thanks!).
---
 lisp/mh-e/mh-comp.el | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lisp/mh-e/mh-comp.el b/lisp/mh-e/mh-comp.el
index 404b6b3..e44c42e 100644
--- a/lisp/mh-e/mh-comp.el
+++ b/lisp/mh-e/mh-comp.el
@@ -638,6 +638,8 @@ See also `mh-compose-forward-as-mime-flag',
 (defun mh-forwarded-letter-subject (from subject)
   "Return a Subject suitable for a forwarded message.
 Original message has headers FROM and SUBJECT."
+  ;; Join continued lines.
+  (setq from (replace-regexp-in-string "\\s *\n\\s +" " " from))
   (let ((addr-start (string-search "<" from))
         (comment (string-search "(" from)))
     (cond ((and addr-start (> addr-start 0))