[gtk+/gtk-3-20] listbox: Avoid crashing on page down if the list has few rows

[Matthias Clasen <matthiasc src gnome org>]

commit eb2a73704b36380c23ab8652f157e9b753c2146f
Author: Joaquim Rocha <jrocha endlessm com>
Date:   Thu Sep 1 13:23:14 2016 +0200

    listbox: Avoid crashing on page down if the list has few rows
    
    The code always assumed that getting a row at a certain 'y' was
    possible but if the list box has more empty space than rows then a
    valid row may not be retrieved.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=770703

 gtk/gtklistbox.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtklistbox.c b/gtk/gtklistbox.c
index 2c21c6d..bcccbcf 100644
--- a/gtk/gtklistbox.c
+++ b/gtk/gtklistbox.c
@@ -3041,10 +3041,11 @@ gtk_list_box_move_cursor (GtkListBox      *box,
           height = gtk_widget_get_allocated_height (GTK_WIDGET (box));
           end_y = CLAMP (start_y + page_size * count, 0, height - 1);
           row = gtk_list_box_get_row_at_y (box, end_y);
-          iter = ROW_PRIV (row)->iter;
 
           if (row == priv->cursor_row)
             {
+              iter = ROW_PRIV (row)->iter;
+
               /* Move at least one row. This is important when the cursor_row's height is
                * greater than page_size */
               if (count < 0)