perf[net]: 修复空指针异常

net/src/main/java/com/zfoo/net/consumer/registry/ZookeeperRegistry.java

@@ -374,6 +374,10 @@ public class ZookeeperRegistry implements IRegistry {
 
     @Override
     public void checkConsumer() {
+        if (curator == null) {
+            return;
+        }
+
         if (curator.getState() == CuratorFrameworkState.STOPPED) {
             return;
         }