bug#74617: 30.0.92; ffap-menu always displays the *Completions* buffer

[Juri Linkov]

> The pattern where completion commands want to display candidates
> immediately is not uncommon. There are ffap, tmm and multiple
> third-party packages which have such a requirement. So I suggest to not
> necessarily treat "immediate candidate display" as a bug report, but
> rather as a feature request for `completing-read'.

And imenu.el calls minibuffer-completion-help conditionally
unless imenu-eager-completion-buffer is not nil.