[gtk+] wayland: fix filechooser crash

[Matthias Clasen <matthiasc src gnome org>]

commit bd033165e52469845ac6f69c4fa9ac9b897f9bcc
Author: Lionel Landwerlin <lionel g landwerlin intel com>
Date:   Wed Aug 23 15:22:47 2017 +0100

    wayland: fix filechooser crash
    
    The opaque region of the window can be updated before we're requested
    its creation on the compositor.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=786673

 gdk/wayland/gdkwindow-wayland.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/gdk/wayland/gdkwindow-wayland.c b/gdk/wayland/gdkwindow-wayland.c
index 1b01534..3da3a9d 100644
--- a/gdk/wayland/gdkwindow-wayland.c
+++ b/gdk/wayland/gdkwindow-wayland.c
@@ -1177,7 +1177,8 @@ gdk_wayland_window_sync_opaque_region (GdkWindow *window)
     wl_region = wl_region_from_cairo_region (GDK_WAYLAND_DISPLAY (gdk_window_get_display (window)),
                                              impl->opaque_region);
 
-  wl_surface_set_opaque_region (impl->display_server.wl_surface, wl_region);
+  if (impl->display_server.wl_surface)
+    wl_surface_set_opaque_region (impl->display_server.wl_surface, wl_region);
 
   if (wl_region != NULL)
     wl_region_destroy (wl_region);