Fix the width of `PhutilConsoleTable` if the header row is wider than the data rows.

Summary:
Currently, the width of the header text is not taken into consideration when drawing the table. The width of the header text must be accounted for as if it were an ordinary row. Specifically, the following error occurs otherwise:

```
PHP Warning:  str_repeat(): Second argument has to be greater than or equal to 0 in /home/joshua/workspace/github.com/phacility/libphutil/src/console/PhutilConsoleTable.php on line 211
```

Test Plan: Drew a table with a really wide header column. verified that no warnings were raised and that the table rendered correctly.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9583