[yelp] view: Add a missing cast

[Michael Catanzaro <mcatanzaro src gnome org>]

commit b49f6eb82b17c7ef265d70e1ba7c527bdcbb9e0d
Author: Michael Catanzaro <mcatanzaro igalia com>
Date:   Tue Dec 12 19:05:52 2017 -0600

    view: Add a missing cast
    
    This avoids triggering -Werror=incompatible-pointer-type after the
    g_object_ref/unref type propagation change.

 libyelp/yelp-view.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libyelp/yelp-view.c b/libyelp/yelp-view.c
index afe22a9..183506e 100644
--- a/libyelp/yelp-view.c
+++ b/libyelp/yelp-view.c
@@ -1215,7 +1215,7 @@ popup_save_image (GtkAction   *action,
     data = g_new0 (YelpSaveData, 1);
     data->orig = g_file_new_for_uri (priv->popup_image_uri);
     data->view = g_object_ref (view);
-    data->window = g_object_ref (window);
+    data->window = g_object_ref (GTK_WINDOW (window));
     g_free (priv->popup_image_uri);
     priv->popup_image_uri = NULL;