[gtksourceview] test-widget: fix a warning

[Sébastien Wilmet <swilmet src gnome org>]

commit c81dbc88f86ee7436267c4ea6cf3ac69c7d54b31
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Tue Sep 9 20:52:27 2014 +0200

    test-widget: fix a warning

 tests/test-widget.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/tests/test-widget.c b/tests/test-widget.c
index b439ae0..5e6fef7 100644
--- a/tests/test-widget.c
+++ b/tests/test-widget.c
@@ -478,12 +478,15 @@ forward_string_clicked_cb (TestWidget *self)
 static void
 open_button_clicked_cb (TestWidget *self)
 {
+       GtkWidget *main_window;
        GtkWidget *chooser;
        gint response;
        static gchar *last_dir;
 
+       main_window = gtk_widget_get_toplevel (GTK_WIDGET (self->priv->view));
+
        chooser = gtk_file_chooser_dialog_new ("Open file...",
-                                              NULL,
+                                              GTK_WINDOW (main_window),
                                               GTK_FILE_CHOOSER_ACTION_OPEN,
                                               "Cancel", GTK_RESPONSE_CANCEL,
                                               "Open", GTK_RESPONSE_OK,