bug#60411: 29.0.60; minibuffer-next-completion skips first candidate when completions-header-format and completion-show-help are nil

[Eli Zaretskii]

> Date: Fri, 06 Jan 2023 08:22:39 +0000
> From: Gregory Heytings <gregory@heytings.org>
> cc: kahatlen@gmail.com, 60411@debbugs.gnu.org, monnier@iro.umontreal.ca, 
>     juri@linkov.net
> 
> >> Stefan and Eli, do you agree with that conclusion?
> >
> > I admit that I've lost the line of reasoning here (too much of the 
> > previous context is being elided, forcing me to re-read the entire 
> > discussion).  Which code is proposed for the release branch, and how 
> > will Emacs behave with that code in this particular use case?
> >
> 
> It's this patch.  It adds an invisible empty line at the beginning of 
> *Completions* when completions-header-format is not a string (in 
> particular, nil) or an empty string.

What is the significance of these two special values of
completions-header-format?  Is it that you want to test whether the
first candidates starts at buffer position 1 in the *Completions*
buffer?  Then why not test for that explicitly?