[gtk+] wayland: check parent surface for subsurface

[Olivier Fourdan <ofourdan src gnome org>]

commit 08aade4b7c4ff011402aada4270a6c4260d30958
Author: Olivier Fourdan <ofourdan redhat com>
Date:   Tue May 16 16:13:34 2017 +0200

    wayland: check parent surface for subsurface
    
    When an event is received while a tooltip is showing, the GtkTooltip's
    event handling code can end up calling gdk_window_set_transient_for()
    from gtk_tooltip_set_last_window().
    
    The Wayland GDK backend will try to automatically create a subsurface
    in gdk_wayland_window_set_transient_for() but if the parent surface is
    gone meanwhile, this will will cause a crash when trying to create a
    subsurface from a parent with a null surface.
    
    Checking for the parent is not sufficient, we ought to check for the
    parent surface as well to avoid the crash.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=782283

 gdk/wayland/gdkwindow-wayland.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gdk/wayland/gdkwindow-wayland.c b/gdk/wayland/gdkwindow-wayland.c
index 95b74df..6e78de8 100644
--- a/gdk/wayland/gdkwindow-wayland.c
+++ b/gdk/wayland/gdkwindow-wayland.c
@@ -1312,7 +1312,7 @@ gdk_wayland_window_create_subsurface (GdkWindow *window)
   if (impl->transient_for)
     parent_impl = GDK_WINDOW_IMPL_WAYLAND (impl->transient_for->impl);
 
-  if (parent_impl)
+  if (parent_impl && parent_impl->display_server.wl_surface)
     {
       display_wayland = GDK_WAYLAND_DISPLAY (gdk_window_get_display (window));
       impl->display_server.wl_subsurface =