Fallback for nnmail-split-methods

[Thomas.Gehrlein@t-online.de (Thomas Gehrlein)]

nnmail-split-fancy has a fallback option for mails that don't match any of the
splitting rules.  nnmail-split-methods doesnt't provide a fallback.  I
discovered this after some of my mails had disappeared.

Here's some code that makes nnmail-split-methods safer.  I'm not really happy
with my approach, but I couldn't figure out how the gnus splitting code works.

(defun nnmail-split-methods-add-fall-back ()
  "Add a fall-back group to nnmail-split-methods if there isn't one."
  ;; check for fall-back: second element of last list of split methods is "".
  (unless (or (eq nnmail-split-methods 'nnmail-split-fancy)
              (string= ""
                       (cadr (elt nnmail-split-methods
                                  (1- (length nnmail-split-methods))))))
    ;; add fall-back if there isn't one
    (setq nnmail-split-methods
          (append nnmail-split-methods (list (list "mail.misc" ""))))))

(add-hook 'nnmail-prepare-incoming-hook 'nnmail-split-methods-add-fall-back)

Thomas