Move call to getMessageHandler().onResynchronize(); to right place

#12043 changed resync message sending to be deferred to queue. Now also the setting of the semaphor in message handler needs to be deferred to its right place. Otherwise there is possibility for a timing glitch. I.e. MessageHandler is set to resync handling mode before message is actually send.

Fixes: #12151

client/src/main/java/com/vaadin/client/communication/MessageSender.java

@@ -127,6 +127,7 @@ private void doSendInvocationsToServer() {
         }
         if (resynchronizeRequested) {
             getLogger().info("Resynchronizing from server");
+            getMessageHandler().onResynchronize();
             extraJson.put(ApplicationConstants.RESYNCHRONIZE_ID, true);
             resynchronizeRequested = false;
         }
@@ -356,7 +357,6 @@ private VLoadingIndicator getLoadingIndicator() {
      * state from the server
      */
     public void resynchronize() {
-        getMessageHandler().onResynchronize();
         getLogger().info("Resynchronize from server requested");
         resynchronizeRequested = true;
         sendInvocationsToServer();