echarts重写图例点击事件

echarts version: 3.1.2

修改图例点击事件样例代码：

• 当第一次点击图例时，只显示点击的图例。
• 当还剩一个图例被取消选中后，自动全选中所有图例。

  var triggerAction = function(action, selected) {        legend = [];        for ( name in selected) {            if (selected.hasOwnProperty(name)) {                legend.push({name: name});            }        }        myChart.dispatchAction({            type: action,            batch: legend        });    };    var isFirstUnSelect = function(selected) {        var unSelectedCount = 0;        for ( name in selected) {            if (!selected.hasOwnProperty(name)) {                continue;            }            if (selected[name] == false) {                ++unSelectedCount;            }        }        return unSelectedCount==1;    };    var isAllUnSelected = function(selected) {        var selectedCount = 0;        for ( name in selected) {            if (!selected.hasOwnProperty(name)) {                continue;            }            // 所有 selected Object 里面 true 代表 selected， false 代表 unselected            if (selected[name] == true) {                ++selectedCount;            }        }        return selectedCount==0;    };    myChart.on('legendselectchanged', function(obj) {        var selected = obj.selected;        var legend = obj.name;        // 使用 legendToggleSelect Action 会重新触发 legendselectchanged Event，导致本函数重复运行        // 使得 无 selected 对象        if (selected != undefined) {            if (isFirstUnSelect(selected)) {                triggerAction('legendToggleSelect', selected);            } else if (isAllUnSelected(selected)) {                triggerAction('legendSelect', selected);            }        }    });