bug#44080: 27.1; Display behavior of overlays `after-string` in resizable minibuffer frames

[Clemens <clemens.radermacher@posteo.de>]

Hi,

there seems to be display bug when using `after-string` to display text 
in resizable minibuffer frames. To reproduce:

1. `emacs -Q --eval "(setq default-frame-alist '((minibuffer . nil)))"`
2. `eval-buffer` with following code:

```elisp
(setq resize-mini-frames t)

(defvar ov (make-overlay (point-min) (point-min) nil t t))

(minibuffer-with-setup-hook
     (lambda ()
       (move-overlay ov
		    (point-max)
		    (point-max)
		    (current-buffer))
        ;; Note the initial newline...
       (overlay-put ov 'after-string "\nHey there, I'm hidden initially 
and will hide again after any space in the input"))
   (read-string "Hi? "))
```

3. Start typing

As stated in the after-string text, it is initially hidden, shows when 
you input some text and gets hidden again every time you type a space.

--

In GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.30, 
cairo version 1.15.10)
  of 2020-08-20 built on clemera
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Ubuntu 18.04.5 LTS

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
user-error: Beginning of history; no preceding item

Configured using:
  'configure --with-modules --with-json --with-cairo'

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

Important settings:
   value of $LC_MONETARY: de_DE.UTF-8
   value of $LC_NUMERIC: de_DE.UTF-8
   value of $LC_TIME: de_DE.UTF-8
   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 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
cairo move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 43837 7270)
  (symbols 48 6003 1)
  (strings 32 15436 1428)
  (string-bytes 1 506267)
  (vectors 16 9260)
  (vector-slots 8 124508 9186)
  (floats 8 19 43)
  (intervals 56 184 0)
  (buffers 1000 11))