fixed cocos2d#2452:optimize javascript code

Author: ShengxiangChen

cocos2d/base_nodes/CCNode.js

@@ -3549,37 +3549,19 @@ cc.NodeCanvas = cc.Class.extend(/** @lends cc.NodeCanvas# */{
         if (len > 0) {
             this.sortAllChildren();
             // draw children zOrder < 0
-            /*var tag = children[0]._zOrder,tmpTag;
-            if(tag >= 0){
-                this.draw();
+            for (i = 0; i < len; i++) {
+                child = children[i];
+                if (child._zOrder < 0)
+                    child.visit(context);
+                else
+                    break;
             }
-            for(i = 0; i < len;i++){
+            this.draw(context);
+            for (; i < len; i++) {
                 child = children[i];
-                tmpTag = child._zOrder;
-                if(tmpTag>=0 && tag < 0){
-                    this.draw();
-                }
-                child.visit(context);
-                tag = tmpTag;
+                if (child._zOrder >= 0)
+                    child.visit(context);
             }
-            if(tag<0){
-                this.draw();
-            }*/
-
-            for (i = 0; i < len; i++) {
-             child = children[i];
-             if (child._zOrder < 0)
-             child.visit(context);
-             else
-             break;
-             }
-             this.draw(context);
-             for (; i < len; i++) {
-             child = children[i];
-             if (child._zOrder >= 0)
-             child.visit(context);
-             }
-
         } else
             this.draw(context);