bug#38992: 27.0.60; when enabled, fido-mode seems to break vc-git-grep

[João Távora]

> [...apropos M-x inside completing minibuffers...]
> This must have changed recently because I
>
> emacs -Q
> M-x fido-mode
> C-x C-f
> M-x ---> error message
>
> On GNU Emacs 27.0.60 (build 2, x86_64-pc-linux-gnu, X toolkit, Xaw3d
> scroll bars) of 2020-02-01

And now I tried in a fresh build of emacs-27 and same behaviour.  I think
it's sane behaviour, by the way.

João