修正了Flex Tree 控件在動態加載節點后 Scrollbar 沒有立即出現的問題

   var _loadSubFolder:Function = function(children:Array):void{
    node.children = new ArrayCollection(children);
    
    for each(var glossaryfolder:Object in node.children){
     if(glossaryfolder.child_count > 0){
      glossaryfolder.children = childrenMark; //replace the template
     }
    }
    
    //very important for showing tree scrollbar.
    var arr:Array = grpTree.openItems as Array;
    var openItems:ArrayCollection = new ArrayCollection(arr);
    for(var i:int=0;i<openItems.length;i++){
     if(openItems[i] == node){
      openItems.removeItemAt(i);
      openItems.refresh();
     }
    }
    grpTree.openItems = openItems.toArray();
    grpTree.expandItem(node, true);
    
    grpTree.invalidateList();
    grpTree.invalidateDisplayList();
   }