bug#23809: 24.5; Positive argument to 'posn-at-point' throws erros as being negative

[Lluís Vilanova]

To reproduce:

* Open a PDF on a separate window on the same frame using pdf-tools.
* Select that window.
* Scroll a bit down the first page of the PDF.
* Use windmove to move from the pdf-view-mode buffer to the first one.


With these steps, I get this backtrace:

  Debugger entered--Lisp error: (wrong-type-argument wholenump -14)
    posn-at-point(619194 #)
    (nth 2 (posn-at-point (window-point window) window))
    (let ((posn-cons (nth 2 (posn-at-point (window-point window) window)))) (if 
hor (+ (or (cdr posn-cons) 1) (window-pixel-top window)) (+ (or (car posn-cons) 
1) (window-pixel-left window))))
    (cond ((and (numberp sign) (< sign 0)) (if hor (1- (+ (window-pixel-top 
window) (window-pixel-height window))) (1- (+ (window-pixel-left window) 
(window-pixel-width window))))) ((and (numberp sign) (> sign 0)) (if hor 
(window-pixel-top window) (window-pixel-left window))) ((let ((posn-cons (nth 2 
(posn-at-point (window-point window) window)))) (if hor (+ (or (cdr posn-cons) 
1) (window-pixel-top window)) (+ (or (car posn-cons) 1) (window-pixel-left 
window))))))
    (let* ((frame (window-frame window)) (hor (memq direction (quote (left 
right)))) (first (if hor (window-pixel-left window) (window-pixel-top window))) 
(last (+ first (window-size window hor t))) (posn (cond ((and (numberp sign) (< 
sign 0)) (if hor (1- (+ ... ...)) (1- (+ ... ...)))) ((and (numberp sign) (> 
sign 0)) (if hor (window-pixel-top window) (window-pixel-left window))) ((let 
((posn-cons ...)) (if hor (+ ... ...) (+ ... ...)))))) (best-edge (cond ((eq 
direction (quote below)) (frame-pixel-height frame)) ((eq direction (quote 
right)) (frame-pixel-width frame)) (t -1))) (best-edge-2 best-edge) 
(best-diff-2 (if hor (frame-pixel-height frame) (frame-pixel-width frame))) 
best best-2 best-diff-2-new) (walk-window-tree (function (lambda (w) (let* 
((w-top (window-pixel-top w)) (w-left (window-pixel-left w))) (cond ((or ... 
...)) (hor (cond ... ...)) ((and ... ...) (if ... ...)) ((and ... ... ...) 
(setq best-edge-2 w-top) (setq best-diff-2 best-diff-2-new) (setq best-2 
w)))))) frame nil (and mini t)) (or best best-2))
    window-in-direction(left nil nil nil nil t)
    windmove-find-other-window(left nil nil)
    windmove-do-window-select(left nil)
    windmove-left(nil)
    #(windmove-left nil nil)
    ad-Advice-call-interactively(# windmove-left nil nil)
    apply(ad-Advice-call-interactively # (windmove-left nil nil))
    call-interactively(windmove-left nil nil)
    command-execute(windmove-left)


Note how the argument to posn-at-point (returned by window-point) is actually
positive (619194), but the error raised by Emacs complains about the number
being negative (-14).

Thanks,
  Lluis


Auto-gathered information:

In GNU Emacs 24.5.1 (x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
 of 2016-04-08 on binet, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11803000
System Description:     Debian GNU/Linux testing (stretch)

Configured using:
 `configure --build x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib
 --libexecdir=/usr/lib --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 
--enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.5/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.5/site-lisp:/usr/share/emacs/site-lisp
 --build x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib
 --libexecdir=/usr/lib --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 
--enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.5/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.5/site-lisp:/usr/share/emacs/site-lisp
 --with-x=yes --with-x-toolkit=gtk3 --with-toolkit-scroll-bars 'CFLAGS=-g -O2
 -fstack-protector-strong -Wformat -Werror=format-security -Wall'
 'CPPFLAGS=-Wdate-time -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

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

Major mode: Debugger

Minor modes in effect:
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  TeX-PDF-mode: 1
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  magit-auto-revert-mode: t
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  auto-compression-mode: t
  buffer-read-only: t
  size-indication-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
Guessed variable 'css-indent-offset' (2)
Ispell process killed
Starting new Ispell process aspell with default dictionary...
Winner undo (1 / 7)
1238378 (#o4562552, #x12e56a)
Type "q" in help window to restore its previous buffer.
Mark set [2 times]
Quit
(#<window 529 on *Backtrace*> 1 (0 . 0) 0 nil 1 (0 . 0) nil (0 . 0) (8 . 14))
nil [3 times]

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