bug#43645: 26.3; emacsclient -c does not open to correct window

[Blue track]

When opening an emacsclient instance to a new intance of a buffer which
is already open, under some conditions it does not open to the correct
buffer.

To reproduce:
```
emacs -Q --daemon

echo "Test" > test.txt
emacsclient -c test.txt
C-x 3
C-x b *scratch*

# In new terminal
emacsclient -c test.txt

# I get a new window with the *scratch* buffer, but under Ubuntu 20.04 the first emacsclient intance is on top also
```


In GNU Emacs 26.3 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.14)
 of 2020-03-26, modified by Debian built on lcy01-amd64-020
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Ubuntu 20.04.1 LTS

Recent messages:
Quit
Undo!
Mark set [2 times]
Quit [4 times]
C-h C-g is undefined
When done with this frame, type C-x 5 0
Quit [2 times]
Mark activated
Mark set
Quit [2 times]
next-line: End of buffer
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/26.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/26.3/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/26.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/26.3/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=/build/emacs-mEZBk7/emacs-26.3+1=. -fstack-protector-strong
 -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

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

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

Major mode: Fundamental

Minor modes in effect:
  recentf-mode: t
  diff-auto-refine-mode: t
  global-so-long-mode: t
  shell-dirtrack-mode: t
  global-undo-tree-mode: t
  ivy-mode: t
  global-hl-line-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort emacsbug sendmail conf-mode dabbrev novice org-table
css-mode misearch multi-isearch org-indent org-rmail org-mhe org-irc
org-info org-gnus nnir gnus-sum gnus-group gnus-undo gnus-start
gnus-cloud nnimap nnmail mail-source tls gnutls utf7 netrc nnoo
gnus-spec gnus-int gnus-range message rmc puny rfc822 mml mml-sec epa
epg epg-config mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader gnus-win gnus nnheader gnus-util rmail
rmail-loaddefs rfc2047 rfc2045 ietf-drums mail-utils mm-util mail-prsvr
org-docview doc-view image-mode org-bibtex bibtex org-bbdb org-w3m
goto-addr view python tramp-sh mail-extr recentf tree-widget wid-edit
bookmark pp autorevert filenotify ffap tramp tramp-compat tramp-loaddefs
trampver ucs-normalize parse-time windmove face-remap flyspell ispell
vc-git diff-mode server elec-pair git-gutter dockerfile-mode sh-script
smie executable s so-long js2-mode etags js sgml-mode dom flycheck json
map subr-x seq jka-compr let-alist dash web-mode disp-table powershell
shell csharp-mode imenu cc-langs cc-mode cc-fonts cc-guess cc-menus
cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs markdown-mode rx
url-parse auth-source password-cache url-vars thingatpt undo-tree diff
counsel xdg xref project eieio byte-opt bytecomp byte-compile cconv
eieio-core eieio-loaddefs dired dired-loaddefs compile swiper cl-extra
help-mode ivy derived delsel ivy-overlay colir org-bullets edmacro
kmacro fill-column-indicator rainbow-delimiters rainbow-mode cl-macs
color cl gv hl-line base16-custom-theme base16-theme pcase org-element
cl-seq avl-tree generator org advice org-macro org-footnote
org-pcomplete pcomplete org-list org-faces org-entities time-date
noutline outline easy-mmode org-version ob-emacs-lisp ob ob-tangle
org-src ob-ref ob-lob ob-table ob-keys ob-exp ob-comint comint
ansi-color ring ob-core ob-eval org-compat org-macs org-loaddefs
format-spec find-func cal-menu easymenu calendar cal-loaddefs
cl-loaddefs cl-lib 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 threads 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 1316058 202171)
 (symbols 48 62374 1)
 (miscs 40 26716 8353)
 (strings 32 155100 14439)
 (string-bytes 1 4894801)
 (vectors 16 97667)
 (vector-slots 8 2404231 18878)
 (floats 8 709 903)
 (intervals 56 51863 1166)
 (buffers 992 115))