Fix alternative-email-as-from with empty To headers in Message

* lisp/gnus/message.el (message-use-alternative-email-as-from):
Don't add a "," at the start of the address if the To header
doesn't exist (bug#34293).

1 files changed, 7 insertions, 1 deletions

diff --git a/lisp/gnus/message.el b/lisp/gnus/message.el
index fbe8b451401..727bbabcb24 100644
--- a/lisp/gnus/message.el
+++ b/lisp/gnus/message.el
@@ -8108,7 +8108,13 @@ From headers in the original article."
          (emails
           (message-tokenize-header
            (mail-strip-quoted-names
-            (mapconcat 'message-fetch-reply-field fields ","))))
+            (mapconcat
+             #'identity
+             (cl-loop for field in fields
+                      for value = (message-fetch-reply-field field)
+                      when value
+                      collect value)
+             ","))))
          (email
           (cond ((functionp message-alternative-emails)
                  (car (cl-remove-if-not message-alternative-emails emails)))