make 0 autosize column width as documented

[disberd]

Currently within the text backend, providing a value of 0 to some of the entries in fixed_data_column_widths does not make the column width size based on the largest cell contradicting the documentation.

This simple PR just update the code to reflects the behavior in the documentation (and modifies a single test to also test providing a 0 instead of a negative number).

I considered updating the documentation, especially because all tests explicitly put -1 for autosizing, but this change would seem more consistent with the behavior when a single Int is provided which actually autosizes for 0

[ronisbr]

Thanks @disberd ! Nice catch.