Correctly handle empty row:
```
% pandoc -f markdown -t rst
+---+---+
| 1 | 2 |
+---+---+
|   |   |
+---+---+
^D
+---+---+
| 1 | 2 |
+---+---+
|   |   |
+---+---+
```

Temporarily added these to figure out what is happening
on Windows builds.
```
% pandoc -f markdown -t native
+---+---+
| 1 | 2 |
+---+---+
|   |   |
+---+---+
^D
[Table [] [AlignDefault,AlignDefault] [5.555555555555555e-2,5.555555555555555e-2]
 [[]
 ,[]]
 [[[Plain [Str "1"]]
  ,[Plain [Str "2"]]]
 ,[[]
  ,[]]]]
```

```
% pandoc -f native -t rst
[Table [] [AlignDefault,AlignDefault] [5.555555555555555e-2,5.555555555555555e-2]
 [[]
 ,[]]
 [[[Para [Str "1"]]
  ,[Para [Str "2"]]]
 ,[[]
  ,[]]]]
^D
+---+---+
| 1 | 2 |
+---+---+
|   |   |
+---+---+
```