bug#22916: 25.0.92; eww completely hangs Emacs on "invalid" png image

[Lars Ljung]

To reproduce: Use eww and go to e.g. http://ttrss.publicplan.de/

The following message is shown in the mini buffer and Emacs hangs with
100% CPU load:

"error in process filter: This Emacs mishandles this image file type"


In GNU Emacs 25.0.92.3 (x86_64-unknown-linux-gnu, GTK+ Version 3.16.7,
cairo version 1.14.2)
 of 2016-03-05 built on kvarnholmen
Repository revision: c45a1ca3c4eed56be6ad8086dcc805a86bc5935c
Windowing system distributor 'The X.Org Foundation', version 11.0.11702000
System Description:     Ubuntu 15.10

Configured using:
 'configure --with-cairo --with-xwidgets --with-modules
 --enable-gcc-warnings'

Configured features:
XPM JPEG TIFF GIF PNG RSVG CAIRO IMAGEMAGICK SOUND GPM DBUS GCONF
GSETTINGS NOTIFY GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 MODULES XWIDGETS

Important settings:
  value of $LC_COLLATE: sv_SE.UTF-8
  value of $LC_CTYPE: sv_SE.UTF-8
  value of $LC_MESSAGES: sv_SE.UTF-8
  value of $LANG: sv_SE.UTF-8
  value of $XMODIFIERS:
  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

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

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message dired format-spec rfc822 mml
mml-sec epg epg-config gnus-util mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util help-fns help-mode easymenu cl-loaddefs pcase
cl-lib mail-prsvr mail-utils time-date mule-util tooltip eldoc electric
uniquify ediff-hook vc-hooks lisp-float-type mwheel x-win
term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list newcomment elisp-mode lisp-mode prog-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core 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 charscript case-table epa-hook jka-cmpr-hook help
simple abbrev 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
dbusbind inotify dynamic-setting system-font-setting font-render-setting
xwidget-internal cairo move-toolbar gtk x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 16 87919 4815)
 (symbols 48 19854 0)
 (miscs 40 377 146)
 (strings 32 14907 4778)
 (string-bytes 1 434882)
 (vectors 16 11989)
 (vector-slots 8 428581 5000)
 (floats 8 164 25)
 (intervals 56 204 0)
 (buffers 976 11)
 (heap 1024 23952 2285))