grid中当初间为空时，正常读取recorde

grid中当时间为空时，正常读取recorde

store的fields和grid中列两者限制一个即可。

举例，让时间字段为空时也能正常显示recorde

,renderer:function (val){if(val && val.time) {            if(Ext.type(val.time) == "string") {            val.time = parseInt(val.time);            }            var d = new Date(val.time);            val = d.format("Y-m-d H:i:s");            } else {            val = "";            }return val;},