bug#38056: 27.0.50; dired.c changes introduced autocompletion error

[Eli Zaretskii <eliz@gnu.org>]

> From: Pankaj Jangid <pankaj.jangid@gmail.com>
> Date: Mon, 04 Nov 2019 10:52:09 +0530
> 
> I have tried it in various ways. The checkin
> 84a3793b194efe92e2eb80cd0f625f3324bf4cae have introduced autocompletion
> issues at various places. To reproduce, I have tried these steps. I have
> also tried it on one previous commit
> (3c86424a182892db1e0216b9aa7e8389ae6f13de). This commit is ok; which
> implies that the issues has occurred in commit
> 84a3793b194efe92e2eb80cd0f625f3324bf4cae only.

FTR, this issue was introduced by commit 0b21ecd, not
84a3793b194efe92e2eb80cd0f625f3324bf4cae.

> (1) launched emacs using "./src/emacs -Q".
> (2) (setq debug-on-error t).
> (3) C-x C-f and then type few characters of some file and TAB. This
> produces same error. autocompletion on directories is working fine.
> OR
> (3) Tried to rename a file in dired. Press R, press few characters of
> the file, press TAB. This produces error. I have debug-on-error set to
> t.
> 
> produces this error:
> 
> Debugger entered--Lisp error: (args-out-of-range "a.txt" 3 2)
>   file-name-completion("a" "~/work/temp/" file-exists-p)

Sorry about that.  Should be fixed now.