Make the current session available in session init listeners (#9946)

Change-Id: I49ec1ed22fb3cae4f2e7ea7e6d989f2157014499

server/src/com/vaadin/server/VaadinService.java

@@ -423,6 +423,8 @@ public abstract class VaadinService implements Serializable {
             throws ServiceException {
         VaadinServiceSession session = createVaadinSession(request);
 
+        VaadinServiceSession.setCurrent(session);
+
         session.storeInSession(this, request.getWrappedSession());
 
         // Initial locale comes from the request