bug#15670: 24.3; dummy user-errors on info nodes without prev/next nodes

[Jarek Czekalski]

When viewing info pages user-errors are generated. I believe they should
not be there. This is a backtrace:

  signal(user-error ("Node has no Next"))
  user-error("Node has no %s" "Next")
  ad-Orig-Info-extract-pointer("next" nil)
  Info-extract-pointer("next")
  Info-check-pointer("next")
  redisplay_internal\ \(C\ function\)()

It's enough to start the info with C-h C-h r or C-h i to
make it happen.

Expected behaviour: no user-errors should be generated, when user makes
no errors.

This was seen when running Emacspeak on Windows.
Dummy error messages cause it to
stop speaking. The log was obtained by putting a backtrace in dtk-stop 
function.


In GNU Emacs 24.3.1 (i386-mingw-nt6.1.7601)
 of 2013-03-17 on MARVIN
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --with-gcc (4.7) --cflags
 -ID:/devel/emacs/libs/libXpm-3.5.8/include
 -ID:/devel/emacs/libs/libXpm-3.5.8/src
 -ID:/devel/emacs/libs/libpng-dev_1.4.3-1/include
 -ID:/devel/emacs/libs/zlib-dev_1.2.5-2/include
 -ID:/devel/emacs/libs/giflib-4.1.4-1/include
 -ID:/devel/emacs/libs/jpeg-6b-4/include
 -ID:/devel/emacs/libs/tiff-3.8.2-1/include
 -ID:/devel/emacs/libs/gnutls-3.0.9/include
 -ID:/devel/emacs/libs/libiconv-1.13.1-1-dev/include
 -ID:/devel/emacs/libs/libxml2-2.7.8/include/libxml2'

Important settings:
  value of $LANG: pl
  locale-coding-system: cp1250
  default enable-multibyte-characters: t

Major mode: Text

Minor modes in effect:
  global-hl-line-mode: t
  recentf-mode: t
  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:
<help-echo> <help-echo> <help-echo> <help-echo> <down-mouse-1>
<mouse-1> <down-mouse-1> <mouse-1> <help-echo> <help-echo>
<help-echo> <help-echo> <help-echo> <help-echo> M-x
r e p o <tab> r t - e m <tab> <return>

Recent messages:
[yas] Prepared just-in-time loading for 
c:/Users/Jarek/AppData/Roaming/.emacs.d/packages/snippets
[yas] Discovered there was already *scratch* in fundamental-mode
[yas] Loading compiled snippets from 
c:/Users/Jarek/AppData/Roaming/.emacs.d/snippets/fundamental-mode
[yas] Prepared just-in-time loading for ~/.emacs.d/snippets
[yas] Reloaded everything (snippets will load just-in-time)....
Loading hl-line...done
Loading whitespace...done
Loading grep...done
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list...

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 grep compile comint ansi-color ring whitespace
hl-line cus-start cus-load yasnippet derived easy-mmode edmacro kmacro
help-mode folding-isearch folding cl-macs gv advice help-fns
advice-preload recentf tree-widget wid-edit easymenu cl cl-lib server
time-date tooltip ediff-hook vc-hooks lisp-float-type mwheel dos-w32
ls-lisp w32-common-fns disp-table w32-win w32-vars 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 w32 multi-tty emacs)
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