Created Issue: Adding more than one chart to worksheet results in corrupt .XLSX file [13181]

I am trying to create an Excel worksheet containing multiple charts. However, when I add a second chart the resulting .XLSX file is corrupt when I try opening it.

Here is a code sample that shows the issue (modified from the LineChart example):

```
static void Main(string[] args)
{
int NUM_OF_CHARTS = 2;

IWorkbook wb = new XSSFWorkbook();
ISheet sheet = wb.CreateSheet("linechart");

IDrawing drawing = sheet.CreateDrawingPatriarch();

for (int i = 0; i < NUM_OF_CHARTS; i++)
{
CreateChart(sheet, drawing, i);
}

using (FileStream fs = File.Create(String.Format("test-{0} charts-{1}.xlsx", NUM_OF_CHARTS, DateTime.Now.Ticks)))
{
wb.Write(fs);
}
}

static IChart CreateChart(ISheet sheet, IDrawing drawing, int factor)
{
int NUM_OF_ROWS = 3;
int NUM_OF_COLUMNS = 10;

Random r = new Random((int)DateTime.Now.Ticks);

System.Threading.Thread.Sleep(r.Next(50, 100));

// Create a row and put some cells in it. Rows are 0 based.
IRow row;
ICell cell;
for (int rowIndex = 0 + (NUM_OF_ROWS * factor); rowIndex < NUM_OF_ROWS * (1 + factor); rowIndex++)
{
row = sheet.CreateRow((short)rowIndex);
for (int colIndex = 0; colIndex < NUM_OF_COLUMNS; colIndex++)
{
cell = row.CreateCell((short)colIndex);
if (rowIndex == 0 + NUM_OF_ROWS * factor)
{
cell.SetCellValue(colIndex);
}
else
{
cell.SetCellValue(r.Next(0,100));
}
}
}

IClientAnchor anchor = drawing.CreateAnchor(0, 0, 0, 0, 10, 0 + (10 * factor), 20, 10 + (10 * factor));

IChart chart = drawing.CreateChart(anchor);
ILineChartData<double, double> data = chart.GetChartDataFactory().CreateLineChartData<double, double>();

// Use a category axis for the bottom axis.
IChartAxis bottomAxis = chart.GetChartAxisFactory().CreateCategoryAxis(AxisPosition.Bottom);
IValueAxis leftAxis = chart.GetChartAxisFactory().CreateValueAxis(AxisPosition.Left);

IChartDataSource<double> xs = DataSources.FromNumericCellRange(sheet, new CellRangeAddress(0 + factor * NUM_OF_ROWS, 0 + factor * NUM_OF_ROWS, 0, NUM_OF_COLUMNS - 1));
IChartDataSource<double> ys1 = DataSources.FromNumericCellRange(sheet, new CellRangeAddress(1 + factor * NUM_OF_ROWS, 1 + factor * NUM_OF_ROWS, 0, NUM_OF_COLUMNS - 1));
IChartDataSource<double> ys2 = DataSources.FromNumericCellRange(sheet, new CellRangeAddress(2 + factor * NUM_OF_ROWS, 2 + factor * NUM_OF_ROWS, 0, NUM_OF_COLUMNS - 1));

var s1 = data.AddSerie(xs, ys1);
s1.SetTitle("title1");
var s2 = data.AddSerie(xs, ys2);
s2.SetTitle("title2");

chart.Plot(data, bottomAxis, leftAxis);

return chart;
}
```




Any ideas?