[ISSUE #4778] Fix Standalone MessageQueue does not down counter when dequeue (#4779)

* bug fix

* bug fix

Author: karsonto

Diff for: eventmesh-storage-plugin/eventmesh-storage-standalone/src/main/java/org/apache/eventmesh/storage/standalone/broker/MessageQueue.java

@@ -236,10 +236,11 @@ private void enqueue(MessageEntity messageEntity) {
      * @return The MessageEntity object at the head of the queue.
      */
     private MessageEntity dequeue() {
-        MessageEntity item = items[takeIndex++];
+        final MessageEntity item = items[takeIndex++];
         if (takeIndex == items.length) {
             takeIndex = 0;
         }
+        count--;
         notFull.signalAll();
         return item;
     }