Refactor Dispatch Start Check for Atomicity

Author: leekib

aws-serverless-java-container-core/src/main/java/com/amazonaws/serverless/proxy/internal/servlet/AwsAsyncContext.java

@@ -69,12 +69,11 @@ public boolean hasOriginalRequestAndResponse() {
     @Override
     public void dispatch() {
         log.debug("Dispatching request");
+
         if (dispatched.get()) {
             throw new IllegalStateException("Dispatching already started");
         }
-        if (!dispatchStarted.get()) {
-            dispatchStarted.set(true);
-        } else {
+        if (dispatchStarted.getAndSet(true)) {
             dispatched.set(true);
             notifyListeners(NotificationType.START_ASYNC, null);
         }