Misaligned separators in grid table
```
% pandoc -f markdown -t html
: Grid Table

+-----------------+:-:+
|Some text        |[text]{.class1 .class2 .class3}|
+-----------------+---+
|Some text        |[text]{.class1 .class2 .class3}|
+-----------------+---+
|Some text        |[text]{.class1 .class2 .class3}|
+-----------------+---+
^D
<table style="width:69%;">
<caption>Grid Table</caption>
<colgroup>
<col style="width: 25%" />
<col style="width: 44%" />
</colgroup>
<tbody>
<tr>
<td>Some text</td>
<td><span class="class1 class2 class3">text</span></td>
</tr>
<tr>
<td>Some text</td>
<td><span class="class1 class2 class3">text</span></td>
</tr>
<tr>
<td>Some text</td>
<td><span class="class1 class2 class3">text</span></td>
</tr>
</tbody>
</table>
```

Missing cell

```
% pandoc -f markdown -t gfm
+------+
| text |
+------+---+
| text | 1 |
+------+---+
^D
|      |     |
|------|-----|
| text |     |
| text | 1   |
```
