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

[Gregory Heytings]

> We could try and add a boolean buffer-local variable to remember if 
> we've already used `minibuffer-next-completion`.  Gregory said he tried 
> and bumped into further problems.  It would arguably be cleaner to do 
> that (and fix whichever other problem shows up), but I haven't had the 
> time to look into that.

In fact, the problem is that buffer-local is not local enough in this 
case, because *Completions* can be reused.  Somehow I did not think of a 
"text-local" variable earlier.