Completion in shell mode fails to find a simple "then" keyword as a
possible completion. Instead, it just lists some executables on the
$PATH starting with the completion text. Those are fine, but I would
expect the "then" keyword to be among the completion possibilities.

This is using Emacs build from master on 2022-01-18, Linux Ubuntu
20.04 running in WSL in Windows 11.

To reproduce:

* Start emacs -Q
* Type C-x C-f foo.sh
* Type "if true; the"
* Type M-: (completion-help-at-point)

Actual Results: (your results will vary; these are executables
beginning with "the" on my $PATH):

  In this buffer, type RET to select the completion near point.

  Possible completions are:
  themecpl.dll
  themeservice.dll
  themeui.dll

Expected results: the keyword "then" should be among the suggested
completion candidates.

In GNU Emacs 29.0.50 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.20,
cairo version 1.16.0)
 of 2022-01-18 built on tower1
Repository revision: f558c35a93de16f21c6a23c8af42fcbc4a617e08
Repository branch: master
System Description: Ubuntu 20.04.3 LTS

Configured using:
 'configure --prefix=/usr/local --with-native-compilation --with-json
 'CFLAGS=-O3 -mtune=native -march=native -fomit-frame-pointer'
 --without-makeinfo'

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

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

Major mode: Shell-script

Minor modes in effect:
  sh-electric-here-document-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-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 mailcap yank-media rmc puny
dired dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg
rfc6068 epg-config gnus-util time-date mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils pcase edebug backtrace
pp cl-print misearch multi-isearch jka-compr find-func cl-extra shortdoc
text-property-search seq completion thingatpt help-fns radix-tree
help-mode cl-loaddefs cl-lib sh-script smie executable term/xterm xterm
gv subr-x byte-opt bytecomp byte-compile cconv iso-transl tooltip eldoc
paren electric uniquify ediff-hook vc-hooks lisp-float-type elisp-mode
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 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 emoji-zwj 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 keymap
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
native-compile emacs)

Memory information:
((conses 16 90451 9251)
 (symbols 48 7360 1)
 (strings 32 24333 2637)
 (string-bytes 1 760555)
 (vectors 16 12189)
 (vector-slots 8 267044 6243)
 (floats 8 75 399)
 (intervals 56 555 0)
 (buffers 992 16))

-- 
Gary