[gtk+] file chooser: Don't pass NULL as title to the portal

[Matthias Clasen <matthiasc src gnome org>]

commit 1e47b9ea67a5eefc255ca2b9199df7e18dc783f8
Author: Matthias Clasen <mclasen redhat com>
Date:   Tue Jun 13 13:09:56 2017 -0400

    file chooser: Don't pass NULL as title to the portal
    
    This causes critical warnings.

 gtk/gtkfilechoosernativeportal.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtkfilechoosernativeportal.c b/gtk/gtkfilechoosernativeportal.c
index 45ceb3f..bf29442 100644
--- a/gtk/gtkfilechoosernativeportal.c
+++ b/gtk/gtkfilechoosernativeportal.c
@@ -288,6 +288,7 @@ show_portal_file_chooser (GtkFileChooserNative *self,
   GDBusMessage *message;
   GVariantBuilder opt_builder;
   gboolean multiple;
+  const char *title;
 
   message = g_dbus_message_new_method_call ("org.freedesktop.portal.Desktop",
                                             "/org/freedesktop/portal/desktop",
@@ -333,10 +334,12 @@ show_portal_file_chooser (GtkFileChooserNative *self,
     g_variant_builder_add (&opt_builder, "{sv}", "choices",
                            serialize_choices (GTK_FILE_CHOOSER_NATIVE (self)));
 
+  title = gtk_native_dialog_get_title (GTK_NATIVE_DIALOG (self));
+
   g_dbus_message_set_body (message,
                            g_variant_new ("(ss@a{sv})",
                                           parent_window_str ? parent_window_str : "",
-                                          gtk_native_dialog_get_title (GTK_NATIVE_DIALOG (self)),
+                                          title ? title : "",
                                           g_variant_builder_end (&opt_builder)));
 
   g_dbus_connection_send_message_with_reply (data->connection,