Avoid Vaadin entry-point being run twice (#13730)

- Prevent bootstrap script fail if registerWidgetset is called twice
  with the same widgetset.

Change-Id: I8b8069b442ea91c1aa0f0b7dd73c41902e75094b

WebContent/VAADIN/vaadinBootstrap.js

@@ -231,13 +231,16 @@
 		loadTheme: loadTheme,
 		registerWidgetset: function(widgetset, callback) {
 			log("Widgetset registered", widgetset);
-			widgetsets[widgetset].callback = callback;
-			for(var i = 0; i < widgetsets[widgetset].pendingApps.length; i++) {
-				var appId = widgetsets[widgetset].pendingApps[i];
-				log("Starting from register widgetset", appId);
-				callback(appId);
+			var ws = widgetsets[widgetset];
+			if (ws && ws.pendingApps) {
+				ws.callback = callback;
+				for(var i = 0; i < ws.pendingApps.length; i++) {
+					var appId = ws.pendingApps[i];
+					log("Starting from register widgetset", appId);
+					callback(appId);
+				}
+				ws.pendingApps = null;
 			}
-			widgetsets[widgetset].pendingApps = null;
 		},
 		getBrowserDetailsParameters: function(parentElementId) {
 			// Screen height and width

client/src/com/vaadin/client/ApplicationConfiguration.java

@@ -222,6 +222,7 @@ public class ApplicationConfiguration implements EntryPoint {
 
     private boolean browserDetailsSent = false;
     private boolean widgetsetVersionSent = false;
+    private static boolean moduleLoaded = false;
 
     static// TODO consider to make this hashmap per application
     LinkedList<Command> callbacks = new LinkedList<Command>();
@@ -596,6 +597,13 @@ public class ApplicationConfiguration implements EntryPoint {
 
     @Override
     public void onModuleLoad() {
+
+        // Don't run twice if the module has been inherited several times.
+        if (moduleLoaded) {
+            return;
+        }
+        moduleLoaded = true;
+
         Profiler.initialize();
         Profiler.enter("ApplicationConfiguration.onModuleLoad");