HTML reader:  Allow space between `<col>` and `</col>`.

Test case:

```
<table border="1">
  <colgroup>
    <col> </col>
    <col></col>
  </colgroup>
  <tbody>
    <tr>
        <td>X</td>
        <td>Y</td>
    </tr>
    <tr>
        <td>1</td>
        <td>2</td>
    </tr>
  </tbody>
</table>

```