bug#38502: 27.0.50; minibuffer-scroll-other-window with multiple frames

[noah <noah.v.peart@gmail.com>]

I think this is new within the last week or so.
When a completion frame pops up while using the minibuffer,
normally the minibuffer-scroll-other-window(-down) functions
scroll the completion window.  However, now when emacs is split
into two horizontal frames, these functions ignore the
completion buffer and scroll the others.

To reproduce from emacs -Q:

    C-x 3
    M-: (mak
    TAB for completions
    C-M-v



In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.30)
 of 2019-12-04 built on noah-M51AC
Repository revision: 23053770449ba1af24961a11d803ae5e948130b6
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Ubuntu 18.04.3 LTS

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Quit [2 times]
Sole completion
Complete, but not unique
Making completion list... [2 times]
Sole completion
Loading /home/noah/.gnus...done
Type C-x 1 to delete the help window.

Configured using:
 'configure --prefix=/usr/local --with-modules --with-xwidgets'

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND GPM DBUS GSETTINGS GLIB NOTIFY INOTIFY
ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS XWIDGETS JSON
PDUMPER LCMS2 GMP

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  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

Load-path shadows:
None found.

Features:
(shadow sort mail-extr cl-extra help-fns radix-tree help-mode emacsbug
message rmc puny dired dired-loaddefs format-spec rfc822 mml easymenu
mml-sec password-cache epa derived epg epg-config gnus-util rmail
rmail-loaddefs text-property-search time-date subr-x seq byte-opt gv
bytecomp byte-compile cconv mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs cl-lib sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils 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 tab-bar menu-bar rfn-eshadow isearch timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame minibuffer 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 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 xwidget-internal move-toolbar
gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 47776 16104)
 (symbols 48 6212 1)
 (strings 32 16512 1685)
 (string-bytes 1 533391)
 (vectors 16 10517)
 (vector-slots 8 134061 14424)
 (floats 8 31 34)
 (intervals 56 225 0)
 (buffers 1000 13))