Avoid an int-conversion error by adding an explicit cast.

Upstream ported this code to C# in:

commit d7095d495c5188856b2c259ce4871f2c64ed0861
Author: Christian Hoff <choff@mono-cvs.ximian.com>
Date:   Tue Mar 17 18:40:35 2009 +0000

    2009-03-17  Christian Hoff  <christian_hoff@gmx.net>
    
            * gdk/Property.custom: add new overloads to the Get method
            for the most common property types
            * gdk/Global.custom: Use the new overloads of Property.Get instead o
f glue
    
    svn path=/trunk/gtk-sharp/; revision=129618

diff --git a/gdk/glue/windowmanager.c b/gdk/glue/windowmanager.c
index 484d713b7e2c9037..0ff11f97d26daa8b 100644
--- a/gdk/glue/windowmanager.c
+++ b/gdk/glue/windowmanager.c
@@ -110,7 +110,7 @@ gtksharp_get_gdk_net_client_list (int *count)
 	list = g_malloc (*count * sizeof (gpointer));
 	/* Put all of the windows into a GList to return */
 	for (i = 0; i < *count; i ++) {
-		list [i] = data [i];
+		list [i] = (gpointer) data [i];
 		g_message ("WinID: %d", list [i]);
 	}