[gtk: 1/2] GdkSurface - Don't call unimplemented NULL set_startup_id() vfunc on Win32

[Matthias Clasen <matthiasc src gnome org>]

commit 2bd6661cd3416ff0a96f4a329ac6bde032f5e33b
Author: Sebastian Dröge <sebastian centricular com>
Date:   Tue May 7 09:53:51 2019 +0300

    GdkSurface - Don't call unimplemented NULL set_startup_id() vfunc on Win32
    
    GdkSurface::set_startup_id() is NULL on Win32 and would cause a segfault
    if called.
    
    While the documentation of the main caller of set_startup_id(),
    gtk_window_set_startup_id(), mentions that it's not implemented on
    Windows it can still be automatically called via Glade and simply doing
    nothing on Win32 is going to be less disruptive than a segfault.

 gdk/gdksurface.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/gdk/gdksurface.c b/gdk/gdksurface.c
index 589a17dfa7..7e95e6a74c 100644
--- a/gdk/gdksurface.c
+++ b/gdk/gdksurface.c
@@ -4202,7 +4202,10 @@ void
 gdk_surface_set_startup_id (GdkSurface   *surface,
                             const gchar *startup_id)
 {
-  GDK_SURFACE_IMPL_GET_CLASS (surface->impl)->set_startup_id (surface, startup_id);
+  GdkSurfaceImplClass *klass = GDK_SURFACE_IMPL_GET_CLASS (surface->impl);
+
+  if (klass->set_startup_id)
+    klass->set_startup_id (surface, startup_id);
 }
 
 /**