bug#42058: Cannot M-x (some?) single-letter commands in ‘fido-mode’

[Dario Gjorgjevski]

Okay, this one is super weird.

To reproduce, launch ‘emacs -Q’ and then

    M-: (defun T () (interactive) (message "T")) RET
    M-x fido-mode RET
    M-x T RET

This results in “Wrong type argument: number-or-marker-p, nil”.  The
issue seems to stem from the fact that

    M-: (read-extended-command) RET
    T RET

returns ‘icomplete-fido-delete-char’ as opposed to ‘T’, which is
returned when ‘fido-mode’ is disabled.

My Emacs version is 28.0.50, built on 2020-06-26 from commit 89c744c380.

Best regards,
Dario

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