bug#50112: 28.0.50; ediff help frame does not display text

[David Phillips via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

I built emacs this morning from the git master branch.
The latest commit was 9b31ad36094666da6b3281025adc163829d89de8 with
a date stamp of Wed Aug 18 20:02:39 2021 +0300.
I am running the macos GUI version.
First I run /Applications/Emacs/Contents/MacOS/Emacs -Q
then I load two files and run 'ediff-buffers' to compare them.
ediff works just fine except that the frame with the help message
is an empty frame. The '?' command changes the frame size but the
text never renders.


In GNU Emacs 28.0.50 (build 1, x86_64-apple-darwin19.6.0, NS appkit-1894.60 Version 10.15.7 (Build 19H1323))
of 2021-08-18 built on Davids-MacBook-Pro.local
Repository revision: 15a8026cafad4a61a2ba5554c1a3e999244e412c
Repository branch: master
Windowing system distributor 'Apple', version 10.3.1894
System Description:  Mac OS X 10.15.7

Configured using:
'configure --with-ns --prefix=/usr/local AR=/usr/bin/ar
RANLIB=/usr/bin/ranlib 'CFLAGS=-I/usr/local/include
-I/usr/local/opt/libxml2/include -I
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/'
'CPPFLAGS=-I/usr/local/include -I/usr/local/opt/libxml2/include -I
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/
-I/usr/local/opt/qt/include -I/usr/local/opt/readline/include
-I/usr/local/opt/libxml2/include' 'LDFLAGS=-L/usr/local/lib
-L/usr/local/opt/qt/lib -L/usr/local/opt/readline/lib
-L/usr/local/opt/libxml2/lib''

Configured features:
ACL DBUS GIF GLIB GMP GNUTLS JPEG JSON LCMS2 LIBXML2 MODULES NOTIFY
KQUEUE NS PDUMPER PNG RSVG THREADS TIFF TOOLKIT_SCROLL_BARS XIM ZLIB

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

Major mode: BSDmakefile

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
  indent-tabs-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
rfc822 mml mml-sec epa derived epg epg-config gnus-util rmail
rmail-loaddefs auth-source cl-seq eieio eieio-core cl-macs
eieio-loaddefs password-cache json map text-property-search time-date
subr-x mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils ediff ediff-merg ediff-mult ediff-wind ediff-diff
ediff-help ediff-init ediff-util vc-git diff-mode easy-mmode
vc-dispatcher cl-loaddefs cl-lib seq byte-opt gv bytecomp byte-compile
cconv make-mode iso-transl tooltip eldoc electric uniquify ediff-hook
vc-hooks lisp-float-type mwheel term/ns-win ns-win ucs-normalize
mule-util term/common-win 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 easymenu
timer select scroll-bar mouse jit-lock font-lock syntax 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 button
loaddefs faces cus-face macroexp files window text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote threads dbusbind kqueue cocoa ns
lcms2 multi-tty make-network-process emacs)

Memory information:
((conses 16 66017 4644)
(symbols 48 8009 1)
(strings 32 23399 1618)
(string-bytes 1 785876)
(vectors 16 16147)
(vector-slots 8 214546 7009)
(floats 8 29 86)
(intervals 56 615 0)
(buffers 992 14))