mu4e-draft/helpers: use newer message-hide-headers

It seems the older (<= emacs 28 at least) message-hide-headers caused
trouble when editing drafts with mu4e in some cases.

So use the _newer_ version of this function, imported as
mu4e--message-hide-headers.

Fixes #2661.

mu4e/mu4e-draft.el

@@ -605,9 +605,11 @@ COMPOSE-TYPE and PARENT are as in `mu4e--draft'."
   ;; now, switch to compose mode
   (mu4e-compose-mode)
 
-  ;; hide some internal headers
+  ;; hide some internal headers; we use the special mu4e-- version of
+  ;; message-hide-headers, since older versions of the latter trigger some bug,
+  ;; #2661.
   (let ((message-hidden-headers mu4e-draft-hidden-headers))
-    (message-hide-headers))
+    (mu4e--message-hide-headers))
 
   ;; hooks
   (add-hook 'before-save-hook  #'mu4e--compose-before-save nil t)

mu4e/mu4e-helpers.el

@@ -31,6 +31,7 @@
 (require 'ido)
 (require 'cl-lib)
 (require 'bookmark)
+(require 'message)
 
 (require 'mu4e-window)
 (require 'mu4e-config)
@@ -576,6 +577,31 @@ This is mu4e's version of Emacs 29's `plistp'."
   (let ((len (proper-list-p object)))
     (and len (zerop (% len 2)))))
 
+(defun mu4e--message-hide-headers ()
+  "Hide headers based on the `message-hidden-headers' variable.
+This is mu4e's version of the post-emacs-28 `message-hide-headers',
+which we need to avoid #2661."
+  (let ((regexps (if (stringp message-hidden-headers)
+                     (list message-hidden-headers)
+                   message-hidden-headers))
+        end-of-headers)
+    (when regexps
+      (save-excursion
+        (save-restriction
+          (message-narrow-to-headers)
+          (setq end-of-headers (point-min-marker))
+          (goto-char (point-min))
+          (while (not (eobp))
+            (if (not (message-hide-header-p regexps))
+                (message-next-header)
+              (let ((begin (point)))
+                (message-next-header)
+                (let ((header (delete-and-extract-region begin (point))))
+                  (save-excursion
+                    (goto-char end-of-headers)
+                    (insert-before-markers header))))))))
+      (narrow-to-region end-of-headers (point-max)))))
+
 (defun mu4e-key-description (cmd)
   "Get the textual form of current binding to interactive function CMD.
 If it is unbound, return nil. If there are multiple bindings,