[gtk] stack: Make the child meta work without stack

[Matthias Clasen <matthiasc src gnome org>]

commit 1632cc7929431082f18f47db15b7a86adb7f3624
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Feb 8 08:22:35 2019 -0500

    stack: Make the child meta work without stack
    
    We have tests that expect this to work, like defaultvalue.

 gtk/gtkstack.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)
---
diff --git a/gtk/gtkstack.c b/gtk/gtkstack.c
index 7ac18bfc79..75bcc69059 100644
--- a/gtk/gtkstack.c
+++ b/gtk/gtkstack.c
@@ -220,8 +220,6 @@ gtk_stack_page_get_property (GObject      *object,
                              GParamSpec   *pspec)
 {
   GtkStackPage *info = GTK_STACK_PAGE (object);
-  GtkWidget *stack = gtk_widget_get_parent (GTK_WIDGET (info->widget));
-  GtkStackPrivate *priv = gtk_stack_get_instance_private (GTK_STACK (stack));
 
   switch (property_id)
     {
@@ -242,7 +240,15 @@ gtk_stack_page_get_property (GObject      *object,
       break;
 
     case CHILD_PROP_POSITION:
-      g_value_set_int (value, g_list_index (priv->children, info));
+      if (info->widget)
+        {
+          GtkWidget *stack = gtk_widget_get_parent (GTK_WIDGET (info->widget));
+          GtkStackPrivate *priv = gtk_stack_get_instance_private (GTK_STACK (stack));
+
+          g_value_set_int (value, g_list_index (priv->children, info));
+        }
+      else
+        g_value_set_int (value, 0);
       break;
 
     case CHILD_PROP_NEEDS_ATTENTION: