[bug] Unexpected behavior when reading data with an uneven numeber of columns per row

I am not 100% sure whether this is a bug or I'm just doing something wrong, but based on the documentation, this behavior should not happen the way it is.

I try to use `datatable` to read DNS zone file data, which has very uneven number on columns per rows but encountered an issue depending on whether the row with the maximum amount columns is part of one of the first rows or not. If that's the case, everything is fine, otherwise `datatable` throws an exception. I already use `fill=True` to fill the missing fields, but this doesn't work.

To reproduce this issue, I created a small repo with code examples and sample data: [scattenlaeufer/datatable_column_error](https://github.com/scattenlaeufer/datatable_column_error)

There is also a small instruction on how to reproduce the issue.

The expected behavior would be for `datatable` to read files with an uneven number of columns in its rows independent on where the line with the most columns is.

My environment is:
- Arch Linux
- Python 3.9.2
- datatable 1.0.0 (current `main` branch)