[gtk/gbsneto/fix-wayland-export-handle] wayland/surface: Only call destroy func when available

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 655c9dd526912cf551865664a03576abdaa9a76a
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Tue Oct 1 11:54:28 2019 -0300

    wayland/surface: Only call destroy func when available
    
    When calling gdk_wayland_surface_export_handle(), if we pass
    some 'user_data' but no 'destroy_func', GTK4 crashes. That's
    because in xdg_exported_handle() we are unconditionally calling
    destroy_func -- even when it's NULL.
    
    Fix that by checking if there's a destroy function before calling
    it.
    
    Fixes https://gitlab.gnome.org/GNOME/gtk/issues/2179

 gdk/wayland/gdksurface-wayland.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/gdk/wayland/gdksurface-wayland.c b/gdk/wayland/gdksurface-wayland.c
index 0a8043b16e..aed4489c7c 100644
--- a/gdk/wayland/gdksurface-wayland.c
+++ b/gdk/wayland/gdksurface-wayland.c
@@ -4063,8 +4063,11 @@ xdg_exported_handle (void                    *data,
   GdkWaylandSurface *impl = GDK_WAYLAND_SURFACE (surface);
 
   impl->exported.callback (surface, handle, impl->exported.user_data);
-  g_clear_pointer (&impl->exported.user_data,
-                   impl->exported.destroy_func);
+  if (impl->exported.destroy_func)
+    {
+      g_clear_pointer (&impl->exported.user_data,
+                       impl->exported.destroy_func);
+    }
 }
 
 static const struct zxdg_exported_v1_listener xdg_exported_listener = {