[gdl] Fix gdk_window_get_origin() assertion in GdlDockMaster.

[Sebastien Granjoux <sgranjoux src gnome org>]

commit 22af5b28bc25e8b1243d75dceda2740d6f43a4a1
Author: Carl-Anton Ingmarsson <ca ingmarsson gmail com>
Date:   Sat Nov 24 00:20:14 2012 +0100

    Fix gdk_window_get_origin() assertion in GdlDockMaster.
    
    Fixes the following assertion in Anjuta
    (lt-anjuta:2876): Gdk-CRITICAL **: gdk_window_get_origin: assertion `GDK_IS_WINDOW (window)' failed
    
    https://bugzilla.gnome.org/show_bug.cgi?id=688961

 gdl/gdl-dock-master.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/gdl/gdl-dock-master.c b/gdl/gdl-dock-master.c
index 77b646e..5bfcb0d 100644
--- a/gdl/gdl-dock-master.c
+++ b/gdl/gdl-dock-master.c
@@ -587,6 +587,9 @@ gdl_dock_master_drag_motion (GdlDockItem *item,
             GdkWindow *dock_window;
             dock = GDL_DOCK (l->data);
             dock_window = gtk_widget_get_window (GTK_WIDGET (dock));
+            if (!dock_window)
+                continue;
+
             /* translate root coordinates into dock object coordinates
                (i.e. widget coordinates) */
             gdk_window_get_origin (dock_window, &win_x, &win_y);