title: Fill up DataGrid with empty rows
body: <p>I have a <code>DataGrid</code> bound to a <code>DataTable</code>. I want the <code>DataGrid</code> to always have at least ten (empty) rows, also if there are not enough real data-items (the data comes in little by little).<br>
  <img src="https://i.stack.imgur.com/ztwbM.png" alt="Example"></p>
  
  <p>One approach would be to easily add ten empty rows to the <code>DataTable</code> at initialization. But when a real data-item comes in, I can't easily add the row, I have to find the first empty row to overwrite it, what is not very handy.<br>
  So someone knows a smarter/built-in way to achieve this?</p>