Preview toggle fix

<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8">
  <title>ZingSoft Demo</title>

  <script nonce="undefined" src="https://cdn.zingchart.com/zingchart.min.js"></script>
  <style>
    html,
    body {
      height: 100%;
      width: 100%;
      margin: 0;
      padding: 0;
    }

    #myChart {
      height: 100%;
      width: 100%;
      min-height: 150px;
    }

    .zc-ref {
      display: none;
    }
  </style>
</head>

<body>
  <button id="demo1">Btn 1</button>
  <div id="myChart"><a class="zc-ref" href="https://www.zingchart.com">Powered by ZingChart</a></div>
  <script>
    ZC.LICENSE = ["569d52cefae586f634c54f86dc99e6a9", "b55b025e438fa8a98e32482b5f768ff5"];
    var myConfig = {
      'type': 'line',
      'series': [{
          "id": 'series1',
          'visible': true,
          'line-color': 'yellow',
          'values': [11, 26, 7, 44, 19]
        },
        {
          "id": 'series2',
          'visible': true,
          'line-color': 'red',
          'values': [18, 12, 27, 34, 21]
        }
      ],
      legend: {
        toggleAction: 'remove'
      },
      preview: {}
    };

    zingchart.render({
      id: 'myChart',
      data: myConfig,
      height: 400,
      width: '100%'
    });

    $('#demo1').bind('click', function() {
      zingchart.exec('myChart', 'modifyplot', {
        'update': true,
        'plotid': 'series2',
        'data': {
          visible: false
        }
      });

      zingchart.exec('myChart', 'reload');
    });
  </script>
</body>

</html>

<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8">
  <title>ZingSoft Demo</title>

  <script src="https://cdn.zingchart.com/zingchart.min.js"></script>
</head>

<body>
  <button id="demo1">Btn 1</button>
  <div id="myChart"><a class="zc-ref" href="https://www.zingchart.com">Powered by ZingChart</a></div>
</body>

</html>

html,
body {
  height: 100%;
  width: 100%;
  margin: 0;
  padding: 0;
}

#myChart {
  height: 100%;
  width: 100%;
  min-height: 150px;
}

.zc-ref {
  display: none;
}

var myConfig = {
  'type': 'line',
  'series': [{
      "id": 'series1',
      'visible': true,
      'line-color': 'yellow',
      'values': [11, 26, 7, 44, 19]
    },
    {
      "id": 'series2',
      'visible': true,
      'line-color': 'red',
      'values': [18, 12, 27, 34, 21]
    }
  ],
  legend: {
    toggleAction: 'remove'
  },
  preview: {}
};

zingchart.render({
  id: 'myChart',
  data: myConfig,
  height: 400,
  width: '100%'
});

$('#demo1').bind('click', function() {
  zingchart.exec('myChart', 'modifyplot', {
    'update': true,
    'plotid': 'series2',
    'data': {
      visible: false
    }
  });

  zingchart.exec('myChart', 'reload');
});