[gtk/gtk-3-24: 1/2] GdkWindow - Don't call unimplemented NULL set_startup_id() vfunc on Win32

[Matthias Clasen <matthiasc src gnome org>]

commit 02d4fbe29e4278c202beaca93d64f1867ca79ac2
Author: Sebastian Dröge <sebastian centricular com>
Date:   Tue May 7 09:59:10 2019 +0300

    GdkWindow - Don't call unimplemented NULL set_startup_id() vfunc on Win32
    
    GdkWindow::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/gdkwindow.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index 14164092d0..6601a32c9c 100644
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -10500,7 +10500,10 @@ void
 gdk_window_set_startup_id (GdkWindow   *window,
                           const gchar *startup_id)
 {
-  GDK_WINDOW_IMPL_GET_CLASS (window->impl)->set_startup_id (window, startup_id);
+  GdkWindowImplClass *klass = GDK_WINDOW_IMPL_GET_CLASS (window->impl);
+
+  if (klass->set_startup_id)
+    klass->set_startup_id (window, startup_id);
 }
 
 /**