bug#26385: Ediff broken

[Richard Copley]

Hi,
Ediff doesn't work, since this commit:

  commit f4b50dad8d5eade04f495c693c0bca46060b25cb
  Author: Philipp Stephani <phst@google.com>
  Date:   Fri Mar 3 18:36:08 2017 +0100

Recipe to reproduce from 'emacs -Q' (assuming 1 and 2 are files that
have differences from one another):

M-x ediff RET
1 RET
2 RET
n

Lisp error: (wrong-type-argument stringp nil)

Lisp backtrace:

  find-file-name-handler(nil file-local-copy)
  file-local-copy(nil)
  #[(bytecode elided)](nil)
  mapcar(#[(bytecode elided)]
("c:/Users/XXX/AppData/Local/Temp/fineDiffA766452D"
"c:/Users/XXX/AppData/Local/Temp/fineDiffB7664GBK" nil))
  ediff-exec-process("diff" #<buffer *ediff-fine-diff*> synchronize
"--binary" "c:/Users/XXX/AppData/Local/Temp/fineDiffA766452D"
"c:/Users/RCO/AppData/Local/Temp/fineDiffB7664GBK" nil)
  
ediff-setup-fine-diff-regions("c:/Users/XXX/AppData/Local/Temp/fineDiffA766452D"
"c:/Users/XXX/AppData/Local/Temp/fineDiffB7664GBK" nil 0)
  ediff-make-fine-diffs(0 noforce)
  ediff-install-fine-diff-if-necessary(0)
  ediff-next-difference(1)
  funcall-interactively(ediff-next-difference 1)
  call-interactively(ediff-next-difference nil nil)
  command-execute(ediff-next-difference)

Reverting the above commit in ediff-diff.el fixes the problem.

In GNU Emacs 26.0.50 (build 1, x86_64-w64-mingw32)
 of 2017-04-06 built on 60678UHB
Repository revision: b286911dc409e3acd2c1f6f33e9ada789d2c7637
Windowing system distributor 'Microsoft Corp.', version 6.1.7601
Recent messages:
Buffer A: Processing difference region 40 of 46
Buffer B: Processing difference region 0 of 46
Buffer B: Processing difference region 10 of 46
Buffer B: Processing difference region 20 of 46
Buffer B: Processing difference region 30 of 46
Buffer B: Processing difference region 40 of 46
Processing difference regions ... done
Refining difference region 1 ...
file-local-copy: Wrong type argument: stringp, nil
Quit this Ediff session? (y or n) y

Configured using:
 'configure --with-modules --without-gnutls --without-pop
 --enable-locallisppath=/c/emacs-lisp CFLAGS=-O3
 PKG_CONFIG_PATH=/mingw64/lib/pkgconfig:/mingw64/share/pkgconfig'

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND DBUS NOTIFY ACL LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS MODULES

Important settings:
  value of $LANG: ENG
  locale-coding-system: cp1252

Major mode: Text

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 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 jka-compr ediff-merg
ediff-wind ediff-diff ediff-mult ediff-help ediff-init cl-loaddefs pcase
cl-lib ediff-util ediff time-date mule-util tooltip eldoc electric
uniquify ediff-hook vc-hooks lisp-float-type mwheel dos-w32 ls-lisp
disp-table term/w32-win w32-win w32-vars term/common-win 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 w32notify dbusbind w32
multi-tty make-network-process emacs)

Memory information:
((conses 16 106111 7287)
 (symbols 56 21265 1)
 (miscs 48 53 128)
 (strings 32 22169 5111)
 (string-bytes 1 704255)
 (vectors 16 15240)
 (vector-slots 8 486224 4828)
 (floats 8 62 124)
 (intervals 56 244 19)
 (buffers 976 16))