[gtk/focus-cleanup] Avoid critical warnings

[Matthias Clasen <matthiasc src gnome org>]

commit 25f4bb2e17e07a8385a927f63635be157db073ad
Author: Matthias Clasen <mclasen redhat com>
Date:   Sun Apr 28 22:55:43 2019 +0000

    Avoid critical warnings
    
    These critical warnings break the tests, otherwise.

 gtk/gtkwidget.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index 4538362107..d95415a515 100644
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -5478,7 +5478,8 @@ static void
 gtk_widget_real_grab_focus (GtkWidget *focus_widget)
 {
   GtkWidgetPrivate *priv = gtk_widget_get_instance_private (focus_widget);
-  gtk_root_set_focus (priv->root, focus_widget);
+  if (priv->root)
+    gtk_root_set_focus (priv->root, focus_widget);
 }
 
 static gboolean