(gnus-data-list nil) does not give valid data sometimes

[Ted Zlatanov <tzz@lifelogs.com>]

The function that fails is:

(defun spam-fetch-field-fast (article field)
  "Fetch a field quickly, using the internal gnus-data-list function"
  (when (numberp article)
    (gnus-get-newsgroup-headers)
    (let* ((header (assoc article (gnus-data-list nil)))
	   (data-header (if header (gnus-data-header header) nil)))
      (if (arrayp data-header)
	(cond
	 ((equal field 'from)
	  (mail-header-from data-header))
	 ((equal field 'message-id)
	  (mail-header-message-id data-header))
	 ((equal field 'subject)
	  (mail-header-subject data-header))
	 ((equal field 'references)
	  (mail-header-references data-header))
	 ((equal field 'date)
	  (mail-header-date data-header))
	 ((equal field 'xref)
	  (mail-header-xref data-header))
	 ((equal field 'extra)
	  (mail-header-extra data-header))
	 (t
	  nil))
	(gnus-error 5 "Article %d has a nil data header" article)))))

When entering a group the first time, lots of errors are generated
above because data-header is nil.  After C-g, the next time the group
is entered everything is fine.  BUT the next time (3rd time) the
group is entered, the errors happen again - and so on, this can be
repeated forever.  I don't use the agent - I'm not sure what's wrong.

This, by the way, is called by spam-insert-fake-headers which is
called by spam-find-spam; spam-find-spam is hooked on
gnus-summary-prepare-hook.

Thanks
Ted