bug#33732: 27.0.50; line-number-current-line face bug

[Jonas Westlund]

When using the built-in display-line-number, placing the point at the
last line of the file/end of buffer will make the rest of
the display-number area adopt the line-number-current-line
face. Modifying the face's background thus produces this kind of effect:

https://i.imgur.com/pO214Wf.png

Steps to reproduce:
1. emacs -Q
2. (setq display-line-numbers t)
3. (set-face-background 'line-number-current-line "#000000")
4. Go to end of buffer


In GNU Emacs 27.0.50 (build 5, x86_64-pc-linux-gnu, GTK+ Version 3.22.30)
of 2018-12-13 built on maskinen
Repository revision: ef922e774ae33772ad86403332ddb5a1b49d268e
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Ubuntu 18.04.1 LTS

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list...
C-M-g is undefined
Quit
Making completion list...
C-M-g is undefined
Quit
Making completion list...

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

Important settings:
value of $LC_CTYPE: en_US.UTF-8
value of $LC_MONETARY: sv_SE.UTF-8
value of $LC_NUMERIC: sv_SE.UTF-8
value of $LC_TIME: sv_SE.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 crm thingatpt emacsbug message rmc puny seq
byte-opt gv bytecomp byte-compile cconv dired dired-loaddefs format-spec
rfc822 mml easymenu mml-sec password-cache epa derived epg epg-config
gnus-util rmail rmail-loaddefs time-date 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
elec-pair 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 97237 13255)
(symbols 48 20303 1)
(strings 32 28883 1218)
(string-bytes 1 759860)
(vectors 16 15095)
(vector-slots 8 511933 16416)
(floats 8 48 69)
(intervals 56 224 0)
(buffers 992 12))