add another test if the pool size is greater than the core pool size before a worker can exit

modules/elasticsearch/src/main/java/org/elasticsearch/common/util/concurrent/TransferThreadPoolExecutor.java

@@ -496,7 +496,7 @@ public class TransferThreadPoolExecutor extends AbstractExecutorService {
         mainLock.lock();
         boolean canExit;
         try {
-            canExit = runState >= STOP || queueSize.get() == 0;
+            canExit = runState >= STOP || (queueSize.get() == 0 && poolSize.get() > corePoolSize);
         } finally {
             mainLock.unlock();
         }