fix node layout error and support subtree

sample/workdir/hero.json

@@ -1 +1,55 @@
-{"name":"hero","root":{"id":1,"name":"Selector","desc":"英雄测试AI","args":{},"children":[{"id":2,"name":"Sequence","desc":"攻击","args":{},"children":[{"id":3,"name":"FindEnemy","args":{"x":0,"y":0,"w":100,"h":50},"output":["enemy"]},{"id":4,"name":"Attack","args":{},"input":["enemy"]},{"id":5,"name":"Wait","args":{"time":10}}]},{"id":6,"name":"Sequence","desc":"移动","args":{},"children":[{"id":7,"name":"FindEnemy","args":{"w":1000,"h":500,"x":0,"y":0},"output":["enemy"]},{"id":8,"name":"MoveToTarget","args":{},"input":["enemy"]}]},{"id":9,"name":"Sequence","desc":"逃跑","args":{},"children":[{"id":10,"name":"GetHp","args":{},"output":["hp"]},{"id":11,"name":"Cmp","args":{"lt":50},"input":["hp"]},{"id":12,"name":"MoveToPos","args":{"x":0,"y":0}}]},{"id":13,"name":"Idle"}]},"desc":"英雄测试AI"}
+{
+    "name": "hero",
+    "root": {
+        "id": 1,
+        "name": "Selector",
+        "desc": "英雄测试AI",
+        "args": {},
+        "children": [
+            {
+                "id": 2,
+                "name": "Sequence",
+                "desc": "攻击",
+                "args": {},
+                "children": [
+                    {
+                        "id": 3,
+                        "name": "FindEnemy",
+                        "args": { "x": 0, "y": 0, "w": 100, "h": 50 },
+                        "output": ["enemy"]
+                    },
+                    { "id": 4, "name": "Attack", "args": {}, "input": ["enemy"] },
+                    { "id": 5, "name": "Wait", "args": { "time": 10 } }
+                ]
+            },
+            {
+                "id": 6,
+                "name": "Sequence",
+                "desc": "移动",
+                "args": {},
+                "children": [
+                    {
+                        "id": 7,
+                        "name": "FindEnemy",
+                        "args": { "w": 1000, "h": 500, "x": 0, "y": 0 },
+                        "output": ["enemy"]
+                    },
+                    { "id": 8, "name": "MoveToTarget", "args": {}, "input": ["enemy"] }
+                ]
+            },
+            {
+                "id": 9,
+                "name": "Sequence",
+                "desc": "逃跑",
+                "args": {},
+                "children": [
+                    { "id": 10, "name": "GetHp", "args": {}, "output": ["hp"] },
+                    { "id": 11, "name": "Cmp", "args": { "lt": 50 }, "input": ["hp"] },
+                    { "id": 12, "name": "MoveToPos", "args": { "x": 0, "y": 0 } }
+                ]
+            },
+            { "id": 13, "name": "Idle" }
+        ]
+    },
+    "desc": "英雄测试AI"
+}