[gtk] treeview: Don't get separator_height more than once

[Timm Bäder <baedert src gnome org>]

commit 7dd54b5789aae821c3af5b5eb9536503832d9e04
Author: Timm Bäder <mail baedert org>
Date:   Tue Jan 15 16:26:13 2019 +0100

    treeview: Don't get separator_height more than once
    
    Closes !209

 gtk/gtktreeview.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/gtk/gtktreeview.c b/gtk/gtktreeview.c
index dc31077220..01f30f5450 100644
--- a/gtk/gtktreeview.c
+++ b/gtk/gtktreeview.c
@@ -5545,6 +5545,7 @@ validate_row (GtkTreeView   *tree_view,
   gboolean is_separator = FALSE;
   gboolean draw_vgrid_lines, draw_hgrid_lines;
   gint expander_size;
+  int separator_height;
 
   /* double check the row needs validating */
   if (! GTK_TREE_RBNODE_FLAG_SET (node, GTK_TREE_RBNODE_INVALID) &&
@@ -5573,6 +5574,8 @@ validate_row (GtkTreeView   *tree_view,
        first_column = first_column->next)
     ;
 
+  separator_height = get_separator_height (tree_view);
+
   context = gtk_widget_get_style_context (GTK_WIDGET (tree_view));
   gtk_style_context_save (context);
   gtk_style_context_add_class (context, GTK_STYLE_CLASS_CELL);
@@ -5604,7 +5607,7 @@ validate_row (GtkTreeView   *tree_view,
 
       if (is_separator)
         {
-          height = get_separator_height (tree_view);
+          height = separator_height;
         }
       else
         {