bug#28862: Emacs 25.3.1 segmentation fault on killing *Colors* buffer

[martin rudalics]

> (add-hook 'delete-frame-functions
>            (lambda (frame)
>              (dolist (elem (window-list frame))
>                (kill-buffer (window-buffer elem)))))

‘delete-frame-functions’ must be used with great care.  For example, I
can crash Emacs 25 by evaluating the following forms in row:

(defvar old-frame (selected-frame))

(defvar new-frame (make-frame))

(add-hook 'delete-frame-functions
          (lambda (f) (delete-frame new-frame)))

(delete-frame old-frame)

Now if killing a buffer in ‘delete-frame-functions’ may delete a frame
because, for example, the buffer is shown in a dedicated window which is
the only window on that frame, you may run exactly in the scenario
described above.  I hopefully fixed that for Emacs 26 so if you could
try the release version ...

martin