added safety to setUserId (when called twice)

Examples/Quill/index.html

@@ -134,11 +134,6 @@
 
     <!-- Create the editor container -->
     <div id="editor">
-      <div>Hello World!</div>
-      <div>Some initial <b>bold</b> text</div>
-      <div>
-        <br>
-      </div>
     </div>
   </div>
 

Examples/Quill/index.js

@@ -8,16 +8,16 @@ Y({
   },
   connector: {
     name: 'websockets-client',
-    room: 'richtext-example17'
-    // debug: true
-    // url: 'http://127.0.0.1:2345'
+    room: 'richtext-example18',
+    debug: true
+    //url: 'http://127.0.0.1:1234'
   },
   sourceDir: '/bower_components',
   share: {
     richtext: 'Richtext' // y.share.richtext is of type Y.Richtext
   }
 }).then(function (y) {
-  window.y = y
+  window.yquill = y
 
   // create quill element
   window.quill = new Quill('#editor', {

y.es6

@@ -64,8 +64,12 @@ module.exports = function (Y/* :any */) {
       return this.y.db.stopGarbageCollector()
     }
     setUserId (userId) {
-      this.userId = userId
-      return this.y.db.setUserId(userId)
+      if (this.userId == null) {
+        this.userId = userId
+        return this.y.db.setUserId(userId)
+      } else {
+        return null
+      }
     }
     onUserEvent (f) {
       this.userEventListeners.push(f)