title: ClosedXML find last row number
body: <p>I'm using ClosedXML with C# to modify an Excel workbook.  I need to find the last row number used but <code>.RowCount()</code> counts how many rows are in the worksheet.  So it is returning 1 million rows when there are only a few thousand.  I have tried <code>LastRowUsed()</code> but that doesn't return an int and there is no <code>.row</code> method for it.  How can I get the last row in an int?</p>