Send WebSocket messages only if connected

app/assets/javascripts/editor/websocket.js

@@ -86,7 +86,11 @@ CommandSocket.prototype.executeCommand = function(cmd) {
  * @param data
  */
 CommandSocket.prototype.send = function(data) {
-  this.websocket.send(data);
+  // Only send message if WebSocket is open and ready.
+  // Ignore all other messages (they might hit a wrong container anyway)
+  if (this.getReadyState() === this.websocket.OPEN) {
+    this.websocket.send(data);
+  }
 };
 
 /**