[shotwell] Fix Fullscreen

[Jens Georg <jensgeorg src gnome org>]

commit fe9bdea99da34fad44864ab9be0a2ae6fd3ab373
Author: Jens Georg <mail+gitkraken jensge org>
Date:   Sat Mar 31 23:27:50 2018 +0200

    Fix Fullscreen
    
    Use the AppWindow for going fullscreen. We are in realize() which would
    need to be finished to have a GdkWindow which we need to get the
    dimensions

 src/Page.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/Page.vala b/src/Page.vala
index 14875f0..50be583 100644
--- a/src/Page.vala
+++ b/src/Page.vala
@@ -2216,7 +2216,7 @@ public abstract class SinglePhotoPage : Page {
     }
     
     public Scaling get_canvas_scaling() {
-        return (get_container() is FullscreenWindow) ? Scaling.for_screen(get_container(), 
scale_up_to_viewport) 
+        return (get_container() is FullscreenWindow) ? Scaling.for_screen(AppWindow.get_instance(), 
scale_up_to_viewport)
             : Scaling.for_widget(viewport, scale_up_to_viewport);
     }