bug#25949: 26.0.50; process-file fails when visiting a file with a quoted file name

[Philipp Stephani <p.stephani2@gmail.com>]

emacs -Q
C-x C-f /:/tmp/foobar.txt (it doesn't matter whether the file exists)
M-: (process-file "true")

will result in an error

Debugger entered--Lisp error: (file-missing "Setting current directory" "No such file or directory" "/:/tmp/")
  call-process("true" nil nil nil)
  apply(call-process "true" nil nil nil nil)
  process-file("true" nil nil nil)
  apply(process-file ("true" nil nil nil))
  file-name-non-special(process-file "true" nil nil nil)
  apply(file-name-non-special process-file "true" nil nil nil nil)
  process-file("true" nil nil nil)
  apply(process-file ("true" nil nil nil))
  tramp-run-real-handler(process-file ("true" nil nil nil))
  tramp-file-name-handler(process-file "true" nil nil nil)
  apply(tramp-file-name-handler process-file "true" nil nil nil nil)
  process-file("true")
  eval((process-file "true") nil)
  eval-expression((process-file "true") nil)
  funcall-interactively(eval-expression (process-file "true") nil)
  call-interactively(eval-expression nil nil)
  command-execute(eval-expression)


In GNU Emacs 26.0.50 (build 10, x86_64-unknown-linux-gnu, GTK+ Version 3.10.8)
 of 2017-03-03 built on localhost
Repository revision: 244de7b0ed3bb23e700c9edef51e413602d8720a
Windowing system distributor 'The X.Org Foundation', version 11.0.11501000
System Description:	Ubuntu 14.04 LTS

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --enable-checking --enable-check-lisp-object-type
 --with-modules 'CFLAGS=-O0 -ggdb3''

Configured features:
XPM JPEG TIFF GIF PNG SOUND GSETTINGS NOTIFY GNUTLS FREETYPE XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 MODULES

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-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

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message puny seq byte-opt subr-x gv
bytecomp byte-compile cl-extra help-mode cconv cl-loaddefs pcase cl-lib
dired dired-loaddefs format-spec rfc822 mml easymenu mml-sec
password-cache epa derived epg epg-config gnus-util rmail rmail-loaddefs
mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils
mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils time-date mule-util tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel term/x-win x-win
term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow isearch timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame cl-generic cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932
hebrew greek romanian slovak czech european ethiopic indian cyrillic
chinese composite charscript case-table epa-hook jka-cmpr-hook help
simple abbrev obarray minibuffer cl-preloaded nadvice loaddefs button
faces cus-face macroexp files text-properties overlay sha1 md5 base64
format env code-pages mule custom widget hashtable-print-readable
backquote inotify dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 16 96482 12339)
 (symbols 48 20188 1)
 (miscs 40 39 156)
 (strings 32 17690 5095)
 (string-bytes 1 576738)
 (vectors 16 14048)
 (vector-slots 8 483315 6318)
 (floats 8 48 68)
 (intervals 56 217 0)
 (buffers 976 12)
 (heap 1024 23865 964))

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