bug#14620: 24.3; ido fails to open file with backslash in name

[Daniel Hackney]

1. Create a file named '/tmp/\bad-name' (using touch(1) or shell
output redirection)

2. Open Emacs with `emacs -Q'

3. "C-x C-f" and open '/tmp/\bad-name'. This works fine.

4. Kill the buffer

5. "M-x ido-mode"

6. "C-x C-f" and try open the file

7. Errors with the message:

    ido-set-current-directory: Wrong type argument: stringp, nil


In GNU Emacs 24.3.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.6.0)
 of 2013-03-30 on priscilla
Windowing system distributor `The X.Org Foundation', version 11.0.11303000
System Description:     Ubuntu 13.04

Important settings:
  value of $LC_CTYPE: en_US.UTF-8
  value of $LC_MONETARY: en_US.UTF-8
  value of $LC_NUMERIC: en_US.UTF-8
  value of $LC_TIME: en_US.UTF-8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
C-x C-f \ <tab> <return> C-x k <return> M-x i d o -
f i <tab> f <tab> <return> C-s C-s C-g C-n M-x i d
e <backspace> o - m <tab> o <tab> <return> C-x C-f
b a d <return> M-x r e p o r <tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
byte-code: End of buffer
Quit
Making completion list...
Ido mode enabled
ido-set-current-directory: Wrong type argument: stringp, nil
user-error: Beginning of history; no preceding item

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils help-mode easymenu misearch multi-isearch ido
time-date tooltip ediff-hook vc-hooks lisp-float-type mwheel x-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list newcomment
lisp-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core frame cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese case-table epa-hook jka-cmpr-hook help simple abbrev
minibuffer loaddefs button faces cus-face macroexp files text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote make-network-process dbusbind
dynamic-setting system-font-setting font-render-setting move-toolbar gtk
x-toolkit x multi-tty emacs)