[gtk+] csswidgetnode: Avoid some unnecessary work

[Timm Bäder <baedert src gnome org>]

commit 2dca8f935c0b63446e52415e45666ce299a68c58
Author: Timm Bäder <mail baedert org>
Date:   Fri Jan 19 09:57:49 2018 +0100

    csswidgetnode: Avoid some unnecessary work
    
    The later code would just ref both styles and not do anything else.

 gtk/gtkcsswidgetnode.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkcsswidgetnode.c b/gtk/gtkcsswidgetnode.c
index 050c391..3b1440d 100644
--- a/gtk/gtkcsswidgetnode.c
+++ b/gtk/gtkcsswidgetnode.c
@@ -99,6 +99,9 @@ gtk_css_widget_node_validate (GtkCssNode *node)
   if (widget_node->widget == NULL)
     return;
 
+  if (node->style == widget_node->last_updated_style)
+    return;
+
   style = gtk_css_node_get_style (node);
 
   gtk_css_style_change_init (&change, widget_node->last_updated_style, style);