[gthumb] image viewer: fixed undo after reverting to last saved image

[Paolo Bacchilega <paobac src gnome org>]

commit 86636f6c3ea5b1f7d2dea29febcc89657cd5c687
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Fri Nov 22 10:11:51 2019 +0100

    image viewer: fixed undo after reverting to last saved image
    
    Add back the image to the history.

 extensions/image_viewer/gth-image-viewer-page.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)
---
diff --git a/extensions/image_viewer/gth-image-viewer-page.c b/extensions/image_viewer/gth-image-viewer-page.c
index c8efc3e3..ddec2092 100644
--- a/extensions/image_viewer/gth-image-viewer-page.c
+++ b/extensions/image_viewer/gth-image-viewer-page.c
@@ -1910,13 +1910,22 @@ static void
 gth_image_viewer_page_real_revert (GthViewerPage *base)
 {
        GthImageViewerPage *self = GTH_IMAGE_VIEWER_PAGE (base);
-       GthImageData       *idata;
+       GthImageData       *last_saved;
 
-       idata = gth_image_history_revert (self->priv->history);
-       if (idata != NULL) {
-               _gth_image_viewer_page_set_image (self, idata->image, idata->requested_size, idata->unsaved);
-               gth_image_data_unref (idata);
-       }
+       last_saved = gth_image_history_revert (self->priv->history);
+       if (last_saved == NULL)
+               return;
+
+       gth_image_history_add_image (self->priv->history,
+                                    last_saved->image,
+                                    last_saved->requested_size,
+                                    last_saved->unsaved);
+       _gth_image_viewer_page_set_image (self,
+                                         last_saved->image,
+                                         last_saved->requested_size,
+                                         last_saved->unsaved);
+
+       gth_image_data_unref (last_saved);
 }