fix issue about init node method in 'exhide' file

If you have more than one tree in one page,  and you include the
'exhide' file, and some one tree's nodes are only leaf node,  there are
some tree 's root node will show wrong line.

js example:

var setting = {
edit: {
enable: false,
drag: {
isCopy: false,
isMove: false
},
showRenameBtn: false,
showRemoveBtn: false
},

data: {
key: {
children: "nodes"
}
},

view: {
showLine: true,
showTitle:false,
showIcon:false,
selectedMulti: false
}
};

var zNodesSystem = [

{name:"System",noR:true,open:true,url:"system/network.asp",target:"mainFrame",nodes:
[

{name:"Network1",noR:true,open:true,url:"system/network1.asp",target:"mainFrame"},

{name:"Network2",noR:true,open:true,url:"system/network2.asp",target:"mainFrame"}
]}
];
var zNodesMux = [

{name:"Program1",open:true,noR:true,url:"mux/program1.asp",target:"mainFrame"},
{name:"Program2
",open:true,noR:true,url:"mux/program1.asp",target:"mainFrame"}
];
$(document).ready(function(){
$.fn.zTree.init($("#treeDemo1"), setting, zNodesSystem);
$.fn.zTree.init($("#treeDemo2"), setting, zNodesMux);
$.fn.zTree.init($("#treeDemo3"), setting, zNodesSystem);
$.fn.zTree.init($("#treeDemo4"), setting, zNodesMux);
});

html example:
<div class="zTreeDemoBackground left" >
<ul id="treeDemo1" class="ztree" style="height:80px"></ul>
<ul id="treeDemo2" class="ztree" style="height:80px"></ul>
<ul id="treeDemo3" class="ztree" style="height:80px"></ul>
<ul id="treeDemo4" class="ztree" style="height:80px"></ul>
</div>