[caribou] caribou-gtk-module: fix build with Vala 0.25.2

[Vadim Rutkovsky <vrutkovsky src gnome org>]

commit e4d8efb0fc289cbf72c233d6fed8ceade2bc276b
Author: Jürg Billeter <j bitron ch>
Date:   Wed Aug 27 11:55:45 2014 +0200

    caribou-gtk-module: fix build with Vala 0.25.2

 modules/gtk3/caribou-gtk-module.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/modules/gtk3/caribou-gtk-module.vala b/modules/gtk3/caribou-gtk-module.vala
index b50522b..ac1830f 100644
--- a/modules/gtk3/caribou-gtk-module.vala
+++ b/modules/gtk3/caribou-gtk-module.vala
@@ -61,7 +61,7 @@ namespace Caribou {
                 return Gdk.FilterReturn.CONTINUE;
 
             Gdk.window_get_user_data (gdkwindow, out data);
-            if (data == null || !(data is Gtk.Window))
+            if (data == null || !(((Object *) data) is Gtk.Window))
                 return Gdk.FilterReturn.CONTINUE;
 
             window = (Gtk.Window *) data;