window: set view visible before show it

Since the move into using GtkBuilder's files the views aren't show
automatically. That's why the setting of the view initially was failing.

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=741003

src/gcal-window.c

@@ -1149,6 +1149,7 @@ gcal_window_set_property (GObject      *object,
     {
     case PROP_ACTIVE_VIEW:
       priv->active_view = g_value_get_enum (value);
+      gtk_widget_show (priv->views[priv->active_view]);
       gtk_stack_set_visible_child (GTK_STACK (priv->views_stack),
                                    priv->views[priv->active_view]);