[gtk/gtk-3-22] Fix incorrect optimization in find_builtin_icon().

[Matthias Clasen <matthiasc src gnome org>]

commit 5aa939dc93a99736232b3a87511e8b78785c13a9
Author: John Lindgren <john jlindgren net>
Date:   Sat Feb 17 22:03:27 2018 -0500

    Fix incorrect optimization in find_builtin_icon().
    
    When we found an icon with exactly the requested size, we'd stop
    searching immediately (good), but we'd neglect to set the returned
    min_difference to 0 (bad).  This caused theme_lookup_icon() to
    prefer other, potentially much worse, matches over the exact one.

 gtk/gtkicontheme.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/gtk/gtkicontheme.c b/gtk/gtkicontheme.c
index 3225567fb9..a90264d876 100644
--- a/gtk/gtkicontheme.c
+++ b/gtk/gtkicontheme.c
@@ -5399,6 +5399,7 @@ find_builtin_icon (const gchar *icon_name,
       
       if (difference == 0)
         {
+          min_difference = 0;
           min_icon = default_icon;
           break;
         }