bug#2448: 23.0.90; sliced Image not redisplayed when scrolling

[Robert Cochran]

> I used insert-sliced-image to display a picture in a buffer so that I
> can use ^P/^N/^F/^B command to navigate around the picture. There is a
> problem when I tried to move the cursor down (^N) past the visual part
> of the image that the adjacent portions of the picture are not
> displayed. Please see the attached screenshot where the area pointed
> by the red arrow is not displayed.

I tried this just now with "GNU Emacs 27.0.50 (build 1,
x86_64-redhat-linux-gnu, X toolkit, Xaw3d scroll bars) of 2018-06-03" on
Fedora 28.

After doing this:

#+BEGIN_SRC emacs-lisp
;; Just a random screenshot that I had laying around
(insert-sliced-image (create-image "~/Pictures/Screenshot from 2016-03-06 
14-18-11.png") "\n\n" nil 50 50)
#+END_SRC

I was able scroll the image around and everything went more-or-less as
expected; I was not able to reproduce the blank areas as pictured in the
original report.

The original report mentions running on Windows ("GNU Emacs 23.0.90.1
(i386-mingw-nt5.1.2600)"), so perhaps this wasn't ever a problem on the
platform I tried.

Other thoughts?

-- 
~Robert Cochran

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