bug#25157: 26.0.50; whitespace-cleanup does not remove single trailing empty line anymore

[Mark Karpov]

The ‘whitespace-cleanup’ command does not remove single trailing empty
line anymore. To reproduce start emacs with -Q flag, open any file and a
single empty training line, like this:

--- start of file
foo

--- end of file

Then call ‘whitespace-cleanup’. Expected result:

--- start of file
foo
--- end of file

Actual result (nothing happens):

--- start of file
foo

--- end of file

This bug does not manifest itself if there are more than one empty line,
i.e.:

--- start of file
foo


--- end of file

(Executing ‘whitespace-cleanup’):

--- start of file
foo
--- end of file

The result is as expected.

In GNU Emacs 26.0.50.5 (x86_64-unknown-linux-gnu, GTK+ Version 3.22.4)
 of 2016-12-10 built on arch
Repository revision: fc0fd24c105bde4c001ebebe4b8b7e1f96cd2871
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
Recent messages:
Indentation setup for shell type bash
next-line: End of buffer [5 times]
Saving file /home/mark/.bash_profile...
Wrote /home/mark/.bash_profile
Saving file /home/mark/.bash_profile...
Wrote /home/mark/.bash_profile
Quit
nil
Saving file /home/mark/.bash_profile...
Wrote /home/mark/.bash_profile

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY ACL GNUTLS LIBXML2 FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11
LIBSYSTEMD

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

Major mode: iλ

Minor modes in effect:
  shell-dirtrack-mode: t
  diff-auto-refine-mode: t
  aggressive-indent-mode: t
  rainbow-delimiters-mode: t
  whitespace-mode: t
  flycheck-color-mode-line-mode: t
  yas-global-mode: t
  yas-minor-mode: t
  vimish-fold-global-mode: t
  vimish-fold-mode: t
  show-paren-mode: t
  rich-minority-mode: t
  minibuffer-electric-default-mode: t
  ivy-mode: t
  global-auto-revert-mode: t
  display-time-mode: t
  delete-selection-mode: t
  cyphejor-mode: t
  ace-popup-menu-mode: t
  smartparens-global-mode: t
  smartparens-mode: t
  flyspell-mode: t
  flyspell-lazy-mode: t
  mk-highlight-line-mode: t
  modalka-mode: t
  hl-todo-mode: t
  flycheck-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  auto-fill-function: do-auto-fill
  transient-mark-mode: t
  auto-fill-mode: 1

Load-path shadows:
None found.

Features:
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ivy-overlay ffap autorevert filenotify time delsel cyphejor
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flyspell-lazy mk-highlight-line mk-global modalka edmacro kmacro
fix-input quail ace-link hl-todo xref project mu4e mu4e-speedbar
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avy-menu avy ring flycheck json map find-func rx subr-x misc server f
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format env code-pages mule custom widget hashtable-print-readable
backquote dbusbind 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 470216 19037)
 (symbols 48 40810 0)
 (miscs 40 87 365)
 (strings 32 91124 7084)
 (string-bytes 1 2627337)
 (vectors 16 70269)
 (vector-slots 8 1777314 201698)
 (floats 8 654 304)
 (intervals 56 368 0)
 (buffers 976 16))