Fix auto-reverting image-mode buffer (bug#21598)

When auto-reverting an image buffer, `image-mode' is not called since
`revert-buffer' is called with `preserve-modes' set to non-nil.

* lisp/image-mode.el (image-after-revert-hook): Check if there is an
image display property for the current buffer before updating it.

1 files changed, 3 insertions, 0 deletions

diff --git a/lisp/image-mode.el b/lisp/image-mode.el
index a18b07ebe6a..f52668536ca 100644
--- a/lisp/image-mode.el
+++ b/lisp/image-mode.el
@@ -784,6 +784,9 @@ Otherwise, display the image by calling `image-mode'"
   (kill-buffer (current-buffer)))
 
 (defun image-after-revert-hook ()
+  ;; Fixes bug#21598
+  (when (not (image-get-display-property))
+    (image-toggle-display-image))
   (when (image-get-display-property)
     (image-toggle-display-text)
     ;; Update image display.