update getWebThreadPool

hippo4j-spring-boot/hippo4j-spring-boot-starter/src/main/java/cn/hippo4j/starter/handler/web/AbstractWebThreadPoolService.java

@@ -38,9 +38,9 @@ public abstract class AbstractWebThreadPoolService implements WebThreadPoolServi
     public Executor getWebThreadPool() {
         if (executor == null) {
             synchronized (AbstractWebThreadPoolService.class) {
+                if (executor == null) {
                     ApplicationContext applicationContext = ApplicationContextHolder.getInstance();
                     WebServer webServer = ((WebServerApplicationContext) applicationContext).getWebServer();
-                if (executor == null) {
                     executor = getWebThreadPoolByServer(webServer);
                 }
             }