[gtk+] treeview: Add an explicit return for clarity

[Matthias Clasen <matthiasc src gnome org>]

commit ee43462d7421fb08fddf2bce0ff5b2c45e3ece96
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Jul 17 18:41:14 2015 -0400

    treeview: Add an explicit return for clarity
    
    I believe that first_column can only ever be NULL here if
    last_column is NULL too, in which case we'd exited already.
    But coverity doesn't see that, so add an explicit exit.

 gtk/gtktreeview.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtktreeview.c b/gtk/gtktreeview.c
index eb77cd1..05ddece 100644
--- a/gtk/gtktreeview.c
+++ b/gtk/gtktreeview.c
@@ -2687,6 +2687,9 @@ gtk_tree_view_size_allocate_columns (GtkWidget *widget,
        first_column = first_column->next)
     ;
 
+  if (first_column == NULL)
+    return;
+
   rtl = (gtk_widget_get_direction (widget) == GTK_TEXT_DIR_RTL);
 
   /* find out how many extra space and expandable columns we have */