[gtk+] animatedstyle: fail to create new style if timestamp goes backwards

[Matthew Watson <watson src gnome org>]

commit 6a88ac3b4cfa8a56f0bbcec66ecb05079d1a4ccd
Author: Matt Watson <mattdangerw gmail com>
Date:   Tue Mar 22 00:54:11 2016 -0700

    animatedstyle: fail to create new style if timestamp goes backwards
    
    With slowdown factor, we will only we be able to handle timestamps
    that monotonically increase.

 gtk/gtkcssanimatedstyle.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkcssanimatedstyle.c b/gtk/gtkcssanimatedstyle.c
index f0246e9..04337e5 100644
--- a/gtk/gtkcssanimatedstyle.c
+++ b/gtk/gtkcssanimatedstyle.c
@@ -467,6 +467,8 @@ gtk_css_animated_style_new_advance (GtkCssAnimatedStyle *source,
   if (timestamp == 0)
     return g_object_ref (source->style);
 
+  gtk_internal_return_val_if_fail (timestamp > source->current_time, NULL);
+
   animations = NULL;
   for (l = source->animations; l; l = l->next)
     {