[gtk+/gtk-3-20] flowbox: Fix get_child_at_index crash with an invalid index

[Debarshi Ray <debarshir src gnome org>]

commit b1524a8adeb02afa062b5a1c8013c6e3a2ff0d41
Author: Debarshi Ray <debarshir gnome org>
Date:   Fri Dec 2 16:38:05 2016 +0100

    flowbox: Fix get_child_at_index crash with an invalid index
    
    https://bugzilla.gnome.org/show_bug.cgi?id=775525

 gtk/gtkflowbox.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtkflowbox.c b/gtk/gtkflowbox.c
index ecec916..49fdb15 100644
--- a/gtk/gtkflowbox.c
+++ b/gtk/gtkflowbox.c
@@ -4321,7 +4321,7 @@ gtk_flow_box_get_child_at_index (GtkFlowBox *box,
   g_return_val_if_fail (GTK_IS_FLOW_BOX (box), NULL);
 
   iter = g_sequence_get_iter_at_pos (BOX_PRIV (box)->children, idx);
-  if (iter)
+  if (!g_sequence_iter_is_end (iter))
     return g_sequence_get (iter);
 
   return NULL;