Preserving zoom of the serial chart across data updates

HTML

<script type="text/javascript" src="https://www.amcharts.com/lib/3/amcharts.js"></script>
<script type="text/javascript" src="https://www.amcharts.com/lib/3/serial.js"></script>
<script type="text/javascript" src="https://www.amcharts.com/lib/3/themes/none.js"></script>
<div id="chartdiv"></div>
<input type="button" value="update data" id="button" onclick="updateData();" />

CSS

body {
    padding: 10px;
    font-family: Verdana;
    font-size: 12px;
}
#chartdiv {
	width	: 100%;
	height	: 500px;
}
#button {
    position: absolute;
    top: 65px;
    left: 70px;
    padding: 15px;
    font-size: 17px;
}

JavaScript

var chart = AmCharts.makeChart("chartdiv", {
		"type": "serial",
		"theme": "none",
		"pathToImages": "http://www.amcharts.com/lib/3/images/",
		"dataDateFormat": "YYYY-MM-DD",
		"valueAxes": [{
			"axisAlpha": 0,
			"position": "left"
		}],
		"graphs": [{
	  "id": "g1",
			"bullet": "round",
			"bulletBorderAlpha": 1,
			"bulletColor": "#FFFFFF",
			"bulletSize": 5,
			"hideBulletsCount": 50,
			"lineThickness": 2,
			"title": "red line",
			"useLineColorForBulletBorder": true,
			"valueField": "value"
		}],
		"chartScrollbar": {
	  "graph": "g1",
	  "scrollbarHeight": 30
	},
		"chartCursor": {
			"cursorPosition": "mouse"
		},
		"categoryField": "date",
		"categoryAxis": {
			"parseDates": true,
			"dashLength": 1,
			"minorGridEnabled": true,
			"position": "top"
		},
		exportConfig:{
		  menuRight: '20px',
		  menuBottom: '50px',
		  menuItems: [{
		  icon: 'http://www.amcharts.com/lib/3/images/export.png',
		  format: 'png'   
		  }]  
		},
		"dataProvider": [{
			"date": "2012-07-27",
			"value": 13
		}, {
			"date": "2012-07-28",
			"value": 11
		}, {
			"date": "2012-07-29",
			"value": 15
		}, {
			"date": "2012-07-30",
			"value": 16
		}, {
			"date": "2012-07-31",
			"value": 18
		}, {
			"date": "2012-08-01",
			"value": 13
		}, {
			"date": "2012-08-02",
			"value": 22
		}, {
			"date": "2012-08-03",
			"value": 23
		}, {
			"date": "2012-08-04",
			"value": 20
		}, {
			"date": "2012-08-05",
			"value": 17
		}, {
			"date": "2012-08-06",
			"value": 16
		}, {
			"date": "2012-08-07",
			"value": 18
		}, {
			"date": "2012-08-08",
			"value": 21
		}, {
			"date": "2012-08-09",
			"value": 26
		}, {
			"date": "2012-08-10",
			"value": 24
		}, {
			"date": "2012-08-11",
			"value": 29
		}, {
			"date": "2012-08-12",
			"value": 32
		}, {
			"date": "2012-08-13",
			"value": 18
		}, {
			"date": "2012-08-14",
			"value": 24
		}, {
			"date": "2012-08-15",
			"value": 22
		}, {
			"date": "2012-08-16",
			"value": 18
		}, {
			"date":...