bug#48356: 28.0.50; choose-completion discards the suffix after the completion boundary

[Juri Linkov]

> As one downside, it brings back behavior described in
> https://debbugs.gnu.org/34517#14. That doesn't seem too critical to me, but
> opinions might vary.

Sadly, this is quite an important case.  Recently Spencer implemented
a way to deselect a candidate in the visible completions list
(minibuffer-visible-completions=t) when the user starts typing
in the minibuffer.  But then the user could change the mind
and still select a candidate.  This would interfere with the
contents of the minibuffer.