bug#33873: 26.1; nxml-mode: C-c C-i says "Not in a start-tag" after an attribute

[Vincent Lefevre]

Open a file containing

<a><b c=""</a>

in nXML mode.

Put the cursor after the second double-quote, and type C-c C-i.
One gets an error "Not in a start-tag".

This is a regression in 26.1.

My bug report for Debian:
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=917314


In GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.2)
 of 2018-12-21, modified by Debian built on zira
Windowing system distributor 'The X.Org Foundation', version 11.0.12003000
System Description:     Debian GNU/Linux buster/sid

Recent messages:
Loading /etc/emacs/site-start.d/50latex-cjk-common.el (source)...done
Loading /etc/emacs/site-start.d/50latex-cjk-thai.el (source)...done
Loading /etc/emacs/site-start.d/50maxima-emacs.el (source)...done
Loading /etc/emacs/site-start.d/50psvn.el (source)...done
Loading /etc/emacs/site-start.d/50python-docutils.el (source)...done
Loading /etc/emacs/site-start.d/50texlive-lang-english.el (source)...done
Loading /etc/emacs/site-start.d/50why3.el (source)...done
Loading /home/vinc17/share/emacs/site-lisp/mutteditor.el (source)...done
Loading time...done
For information about GNU Emacs and the GNU system, type C-h C-a.

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 --enable-libsystemd --with-pop=yes
 
--enable-locallisppath=/etc/emacs:/usr/local/share/emacs/26.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/26.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --build
 x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib
 --libexecdir=/usr/lib --localstatedir=/var/lib
 --infodir=/usr/share/info --mandir=/usr/share/man --enable-libsystemd
 --with-pop=yes
 
--enable-locallisppath=/etc/emacs:/usr/local/share/emacs/26.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/26.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --with-x=yes
 --with-x-toolkit=gtk3 --with-toolkit-scroll-bars 'CFLAGS=-g -O2
 -fdebug-prefix-map=/tmp/mkdebs-pdkphphb/emacs-26.1+1=.
 -fstack-protector-strong -Wformat -Werror=format-security -Wall'
 'CPPFLAGS=-Wdate-time -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 THREADS LIBSYSTEMD LCMS2

Important settings:
  value of $LC_COLLATE: POSIX
  value of $LC_CTYPE: en_US.UTF-8
  value of $LC_TIME: en_DK
  value of $LANG: POSIX
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  display-time-mode: t
  show-paren-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-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
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
/usr/share/emacs/site-lisp/llvm-3.5/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-3.6/tablegen-mode
/usr/share/emacs/site-lisp/llvm-3.5/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-3.6/llvm-mode
/usr/share/emacs/site-lisp/llvm-3.5/emacs hides 
/usr/share/emacs/site-lisp/llvm-3.6/emacs
/usr/share/emacs/site-lisp/llvm-3.5/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-3.7/tablegen-mode
/usr/share/emacs/site-lisp/llvm-3.5/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-3.7/llvm-mode
/usr/share/emacs/site-lisp/llvm-3.5/emacs hides 
/usr/share/emacs/site-lisp/llvm-3.7/emacs
/usr/share/emacs/site-lisp/llvm-3.5/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-3.8/tablegen-mode
/usr/share/emacs/site-lisp/llvm-3.5/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-3.8/llvm-mode
/usr/share/emacs/site-lisp/llvm-3.5/emacs hides 
/usr/share/emacs/site-lisp/llvm-3.8/emacs
/usr/share/emacs/site-lisp/llvm-3.5/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-3.9/tablegen-mode
/usr/share/emacs/site-lisp/llvm-3.5/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-3.9/llvm-mode
/usr/share/emacs/site-lisp/llvm-3.5/emacs hides 
/usr/share/emacs/site-lisp/llvm-3.9/emacs
/usr/share/emacs/site-lisp/llvm-3.5/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-4.0/tablegen-mode
/usr/share/emacs/site-lisp/llvm-3.5/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-4.0/llvm-mode
/usr/share/emacs/site-lisp/llvm-3.5/emacs hides 
/usr/share/emacs/site-lisp/llvm-4.0/emacs
/usr/share/emacs/site-lisp/rst hides /usr/share/emacs/26.1/lisp/textmodes/rst
/usr/share/emacs/site-lisp/latex-cjk-thai/thai-word hides 
/usr/share/emacs/26.1/lisp/language/thai-word

Features:
(shadow sort mail-extr warnings emacsbug message rmc puny seq byte-opt
gv bytecomp byte-compile 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 elec-pair time cus-start cus-load paren
cc-styles cc-align cc-engine cc-vars cc-defs edmacro kmacro cl-loaddefs
cl-lib time-date mule-util tooltip eldoc electric uniquify ediff-hook
vc-hooks lisp-float-type mwheel term/x-win x-win term/common-win x-dnd
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 charprop
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 dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting move-toolbar gtk
x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 118531 5206)
 (symbols 48 23199 1)
 (miscs 40 55 83)
 (strings 32 34944 1419)
 (string-bytes 1 945950)
 (vectors 16 15938)
 (vector-slots 8 510922 5726)
 (floats 8 56 61)
 (intervals 56 279 0)
 (buffers 992 12))