[libdazzle] animation: add some warnings

[Christian Hergert <chergert src gnome org>]

commit 221604bccad327c2c1ef004bf118ac58dd9cc037
Author: Christian Hergert <chergert redhat com>
Date:   Thu Jun 14 03:42:59 2018 -0700

    animation: add some warnings
    
    I'd like to make sure we've successfully tracked down a weird error, so
    adding this warning in case we find anything new.

 src/animation/dzl-animation.c | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/src/animation/dzl-animation.c b/src/animation/dzl-animation.c
index 629f679..745aafd 100644
--- a/src/animation/dzl-animation.c
+++ b/src/animation/dzl-animation.c
@@ -63,6 +63,7 @@ struct _DzlAnimation
   GdkFrameClock     *frame_clock;         /* An optional frame-clock for sync. */
   GDestroyNotify     notify;              /* Notify callback */
   gpointer           notify_data;         /* Data for notify */
+  guint              stop_called : 1;
 };
 
 G_DEFINE_TYPE (DzlAnimation, dzl_animation, G_TYPE_INITIALLY_UNOWNED)
@@ -687,6 +688,11 @@ dzl_animation_stop (DzlAnimation *animation)
   if (animation == NULL)
     return;
 
+  g_return_if_fail (DZL_IS_ANIMATION (animation));
+  g_return_if_fail (animation->stop_called == FALSE);
+
+  animation->stop_called = TRUE;
+
   if (animation->tween_handler)
     {
       if (animation->frame_clock)