This is a small revision to the `move_cursor_to_start_of_ps1` function described in [‘When did I run that command?’](https://redandblack.io/blog/2020/bash-prompt-with-updating-time/). The original relies on a specific number of lines in `PS1`; this works with an arbitrary number of lines.

The original code works correctly for the `PS1` provided in the article, but [my `PS1`](https://github.com/stilist/dotfiles/blob/81b15068be2f74e44c790a5e295c4c4594869655/dot_prompt#L190-L210) has an additional line, and I wanted to avoid using a [magic number](https://en.wikipedia.org/w/index.php?title=Magic_number_(programming)&oldid=948227984#Unnamed_numerical_constants) in case I change my `PS1` in the future.