[geary] Fix main window showing a menubar under earlier GTK versions.

[Michael Gratton <mjog src gnome org>]

commit 062f8205a27e9e643d7eb2893485d7d47fb51416
Author: Michael James Gratton <mike vee net>
Date:   Fri Dec 9 15:57:35 2016 +1100

    Fix main window showing a menubar under earlier GTK versions.
    
    * src/client/components/main-window.vala (MainWindow::MainWindow):
      Restore explictly setting show-menubar property to false.

 src/client/components/main-window.vala | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/src/client/components/main-window.vala b/src/client/components/main-window.vala
index e6577fa1..6bc3a837 100644
--- a/src/client/components/main-window.vala
+++ b/src/client/components/main-window.vala
@@ -88,6 +88,11 @@ public class MainWindow : Gtk.ApplicationWindow, Geary.BaseInterface {
         Object(application: application);
         base_ref();
 
+        // GTK+ 3.14 (and others?) ignores this property in the UI
+        // file, so set it explicitly here to avoid having a menubar
+        // appear when the desktop shell does not show the app menu
+        this.show_menubar = false;
+
         load_config(application.config);
         restore_saved_window_state();