Subject: 27.0.50; comma inserted at the beginning of email address

From: Juri Linkov <[email-masked]>
Date: Sat, 02 Feb 2019 22:50:24 +0200

X-Debbugs-Package: gnus
X-Debbugs-Version: 5.13

I have customized 'message-alternative-emails' to a regexp that
matches email aliases, but when a email lacks the 'To:' field,
message-use-alternative-email-as-from doesn't remove
the leading ',' prepended due to the empty 'To' field:

(defun message-use-alternative-email-as-from ()
  ...
  (let* ((fields '("To" "Cc" "From"))
	 (emails
	  (message-tokenize-header
	   (mail-strip-quoted-names
	    (mapconcat 'message-fetch-reply-field fields ","))))
  ...

As a result, a comma is added to the beginning of email address.

Commit 357ae5dba5f from 2016-02-08 is a relatively recent change,
and it seems that this bug crept in from this commit.