[gtk+] centerbox: Avoid accessing unset widgets

[Matthias Clasen <matthiasc src gnome org>]

commit 82eafb8a2c6c5aaccff090d9a83110640148b75a
Author: Timm Bäder <mail baedert org>
Date:   Sat Jul 1 18:15:41 2017 +0200

    centerbox: Avoid accessing unset widgets

 gtk/gtkcenterbox.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtkcenterbox.c b/gtk/gtkcenterbox.c
index 2e15f04..4a65b9d 100644
--- a/gtk/gtkcenterbox.c
+++ b/gtk/gtkcenterbox.c
@@ -448,7 +448,7 @@ gtk_center_box_size_allocate (GtkWidget     *widget,
 
       for (i = 0; i < 3; i++)
         {
-          if (gtk_widget_get_valign (child[i]) == GTK_ALIGN_BASELINE)
+          if (child[i] && gtk_widget_get_valign (child[i]) == GTK_ALIGN_BASELINE)
             {
               int child_min_height, child_nat_height;
               int child_min_baseline, child_nat_baseline;