[gtk+] stack: Fix under transitions

[Matthias Clasen <matthiasc src gnome org>]

commit c8ca43ad5148ca380b3525ea1da0c5673e9d9c60
Author: Timm Bäder <mail baedert org>
Date:   Sat Jul 1 19:15:01 2017 +0200

    stack: Fix under transitions
    
    make sure we initialize both width and height with proper values.

 gtk/gtkstack.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkstack.c b/gtk/gtkstack.c
index baa56d4..b1d515a 100644
--- a/gtk/gtkstack.c
+++ b/gtk/gtkstack.c
@@ -1840,6 +1840,9 @@ gtk_stack_snapshot_under (GtkWidget   *widget,
 
   gtk_widget_get_content_size (widget, &widget_width, &widget_height);
   x = y = 0;
+  width = widget_width;
+  height = widget_height;
+
   pos_x = pos_y = 0;
 
   switch (priv->active_transition_type)