Reset window scroll when displaying an image

When viewing a large image full size and scrolling, for instance, to
the lower right corner, then selecting a much smaller image in the
thumbnail buffer, the window stays scrolled so the new image is out of
the window.  One must scroll back to the "origin" to view the new
displayed image, or just kill the image-dired-display-image buffer and
try again.  This fixes the issue.
* lisp/image-dired.el (image-dired-display-window-width):
(image-dired-display-window-height): Operate on a window as argument.
(image-dired-display-image): Bind (image-dired-display-window) and use
it. Set window vscroll and hscroll to zero when refreshing the
buffer's contents.

lisp/image-dired.el

@@ -1674,14 +1674,14 @@ Ask user how many thumbnails should be displayed per row."
              (equal (window-buffer window) buf))))
       (error "No thumbnail image at point"))))
 
-(defun image-dired-display-window-width ()
-  "Return width, in pixels, of image-dired's image display window."
-  (- (image-dired-window-width-pixels (image-dired-display-window))
+(defun image-dired-display-window-width (window)
+  "Return width, in pixels, of WINDOW."
+  (- (image-dired-window-width-pixels window)
      image-dired-display-window-width-correction))
 
-(defun image-dired-display-window-height ()
-  "Return height, in pixels, of image-dired's image display window."
-  (- (image-dired-window-height-pixels (image-dired-display-window))
+(defun image-dired-display-window-height (window)
+  "Return height, in pixels, of WINDOW."
+  (- (image-dired-window-height-pixels window)
      image-dired-display-window-height-correction))
 
 (defun image-dired-display-image (file &optional original-size)
@@ -1697,13 +1697,14 @@ original size."
   (image-dired--check-executable-exists
    'image-dired-cmd-create-temp-image-program)
   (let ((new-file (expand-file-name image-dired-temp-image-file))
+        (window (image-dired-display-window))
         width height command ret
         (image-type 'jpeg))
     (setq file (expand-file-name file))
     (if (not original-size)
         (progn
-          (setq width (image-dired-display-window-width))
-          (setq height (image-dired-display-window-height))
+          (setq width (image-dired-display-window-width window))
+          (setq height (image-dired-display-window-height window))
           (setq command
                 (format-spec
                  image-dired-cmd-create-temp-image-options
@@ -1725,6 +1726,8 @@ original size."
         (clear-image-cache)
         (image-dired-insert-image image-dired-temp-image-file image-type 0 0)
         (goto-char (point-min))
+        (set-window-vscroll window 0)
+        (set-window-hscroll window 0)
         (image-dired-update-property 'original-file-name file)))))
 
 (defun image-dired-display-thumbnail-original-image (&optional arg)