[581266] Validation action should be disabled until there is a selection

Otherwise we get this when the action is run without a selection:
NullPointerException: Cannot invoke "java.util.List.size()" because
"this.selectedObjects" is null
diff --git a/plugins/org.eclipse.emf.edit.ui/src/org/eclipse/emf/edit/ui/action/ValidateAction.java b/plugins/org.eclipse.emf.edit.ui/src/org/eclipse/emf/edit/ui/action/ValidateAction.java
index 60f30d0..004650b 100644
--- a/plugins/org.eclipse.emf.edit.ui/src/org/eclipse/emf/edit/ui/action/ValidateAction.java
+++ b/plugins/org.eclipse.emf.edit.ui/src/org/eclipse/emf/edit/ui/action/ValidateAction.java
@@ -161,6 +161,7 @@
   {
     super(EMFEditUIPlugin.INSTANCE.getString("_UI_Validate_menu_item"));
     setDescription(EMFEditUIPlugin.INSTANCE.getString("_UI_Validate_simple_description"));
+    setEnabled(false);
   }
 
   @Override