Reset reconnect counter when connection is re-established (#11733)

Change-Id: Ifb9895ebdfb6c193ed26c529237423275f0ffd11

client/src/com/vaadin/client/communication/ReconnectingCommunicationProblemHandler.java

         }
 
         reconnectionCause = null;
+        reconnectAttempt = 0;
         hideDialog();
 
         getLogger().info("Re-established connection to server");