bug#50564: 28.0.50; Display artifacting in package list

[Po Lu]

If you move to the end of a truncated line in the package list, part of
the previous screen will be retained when it should actually be
invisible.

To reproduce this problem, start emacs -Q, select the entry "news" from
the package finder (the command finder-by-keyword), then turn on
truncate-lines (if it is not already on) in the package list containing
results from the finder, resize the window showing the package list so
that lines are being truncated, and move to the end of a truncated line.

This problem is not present in Emacs 27.2, and cannot be reproduced on a
TTY frame.

Parts of the previous content of the display will be preserved, which go
away upon invoking redraw-display.

In GNU Emacs 28.0.50 (build 1, i386-pc-solaris2.11, X toolkit, Xaw scroll bars)
 of 2021-09-13 built on blaster
Repository revision: fd1379a85aafa77c119b9b7aa811f669c575bac7
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101001
Configured using:
 'configure --with-gnutls=ifavailable --disable-acl'

Configured features:
GIF JPEG MODULES PDUMPER PNG THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE
XIM XPM LUCID ZLIB

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

Major mode: Package Menu

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
  buffer-read-only: 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 rfc6068 epg-config gnus-util rmail
rmail-loaddefs text-property-search time-date mm-decode mm-bodies
mm-encode mailabbrev gmm-utils mailheader sendmail mail-utils misearch
multi-isearch finder finder-inf find-func lisp-mnt mail-parse rfc2231
rfc2047 rfc2045 mm-util ietf-drums mail-prsvr package browse-url url
url-proxy url-privacy url-expand url-methods url-history url-cookie
url-domsuf url-util mailcap url-handlers url-parse auth-source cl-seq
eieio eieio-core cl-macs eieio-loaddefs password-cache json subr-x map
url-vars seq byte-opt gv bytecomp byte-compile cconv cl-loaddefs cl-lib
iso-transl 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 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
dynamic-setting x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 8 65716 10179)
 (symbols 24 7850 0)
 (strings 16 24023 1996)
 (string-bytes 1 743440)
 (vectors 8 16426)
 (vector-slots 4 249899 19216)
 (floats 8 29 22)
 (intervals 28 609 3)
 (buffers 564 12))