[gtk+] wayland: fix crash in gdk_window_wayland_get_root_coords().

[Christian Hergert <chergert src gnome org>]

commit 5add9625e2ecf153e662a44a7373d8ea624484fc
Author: Christian Hergert <christian hergert me>
Date:   Fri Aug 30 00:23:56 2013 -0700

    wayland: fix crash in gdk_window_wayland_get_root_coords().
    
    Both root_x and root_y may be NULL, so check first before setting.

 gdk/wayland/gdkwindow-wayland.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/gdk/wayland/gdkwindow-wayland.c b/gdk/wayland/gdkwindow-wayland.c
index d2d0b64..52b6136 100644
--- a/gdk/wayland/gdkwindow-wayland.c
+++ b/gdk/wayland/gdkwindow-wayland.c
@@ -1269,8 +1269,11 @@ gdk_window_wayland_get_root_coords (GdkWindow *window,
 
   _gdk_wayland_window_offset (window, &x_offset, &y_offset);
 
-  *root_x = x_offset + x;
-  *root_y = y_offset + y;
+  if (root_x)
+    *root_x = x_offset + x;
+
+  if (root_y)
+    *root_y = y_offset + y;
 
   return 1;
 }