fix the bug for xml namespace not in root

when the namespace is not in the root like

```xml
<root>
<h:table xmlns:h="http://www.w3.org/TR/html4/">
  <h:tr>
    <h:td>Apples</h:td>
    <h:td>Bananas</h:td>
  </h:tr>
</h:table>
</root>
```

it reports error for `split_array[1]`, one check is added before this

test case is added to verify this

it is related with #17 , when `--strip_namespace` is used, the attribute is removed as well, not perfect, but it is good enough for my case.

Handling namespace/attribute different needs more codes