Remove redundant operation when adding child node in NodeSelectorSlot (#794)

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/nodeselector/NodeSelectorSlot.java

@@ -15,9 +15,6 @@
  */
 package com.alibaba.csp.sentinel.slots.nodeselector;
 
-import java.util.HashMap;
-import java.util.Map;
-
 import com.alibaba.csp.sentinel.context.Context;
 import com.alibaba.csp.sentinel.context.ContextUtil;
 import com.alibaba.csp.sentinel.node.ClusterNode;
@@ -26,6 +23,9 @@ import com.alibaba.csp.sentinel.node.EntranceNode;
 import com.alibaba.csp.sentinel.slotchain.AbstractLinkedProcessorSlot;
 import com.alibaba.csp.sentinel.slotchain.ResourceWrapper;
 
+import java.util.HashMap;
+import java.util.Map;
+
 /**
  * </p>
  * This class will try to build the calling traces via
@@ -160,9 +160,10 @@ public class NodeSelectorSlot extends AbstractLinkedProcessorSlot<Object> {
                     cacheMap.putAll(map);
                     cacheMap.put(context.getName(), node);
                     map = cacheMap;
+                    // Build invocation tree
+                    ((DefaultNode) context.getLastNode()).addChild(node);
                 }
-                // Build invocation tree
-                ((DefaultNode)context.getLastNode()).addChild(node);
+
             }
         }