bug#22825: 25.0.91; 'C-h c' doesn't show echo for prefix keys

[Eli Zaretskii <eliz@gnu.org>]

To reproduce:

  emacs -Q
  C-h c C-x

The expected result is to show this in the echo area:

 Describe key (or clock or menu item): C-x-

But what happens in fact on the current emacs-25 branch is that the
echo area is cleared, and the cursor is displayed at its beginning.

Stefan, this started happening on Feb 25th, so I suspect the changes
you made in commit 5244db2 the day before are the culprit.


In GNU Emacs 25.0.91.36 (i686-pc-mingw32)
 of 2016-02-27 built on HOME-C4E4A596F7
Repository revision: 098d47bcf735a1a194a155a8d365746a364617d8
Windowing system distributor 'Microsoft Corp.', version 5.1.2600
Configured using:
 'configure --prefix=/d/usr --enable-checking=yes,glyphs --with-wide-int
 --with-modules 'CFLAGS=-O0 -gdwarf-4 -g3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY ACL GNUTLS LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS MODULES

Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1255

Major mode: Lisp Interaction

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
  transient-mark-mode: t

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

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message dired format-spec rfc822 mml
mml-sec epg epg-config gnus-util mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util help-fns help-mode easymenu cl-loaddefs pcase
cl-lib mail-prsvr mail-utils time-date mule-util tooltip eldoc electric
uniquify ediff-hook vc-hooks lisp-float-type mwheel dos-w32 ls-lisp
disp-table w32-win w32-vars term/common-win tool-bar dnd fontset image
regexp-opt fringe tabulated-list newcomment elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core 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 charscript case-table epa-hook
jka-cmpr-hook help simple abbrev 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 w32notify w32 multi-tty
make-network-process emacs)

Memory information:
((conses 16 93083 5946)
 (symbols 56 20680 0)
 (miscs 48 36 108)
 (strings 16 17732 6334)
 (string-bytes 1 439353)
 (vectors 16 12317)
 (vector-slots 8 421763 4697)
 (floats 8 162 175)
 (intervals 40 262 118)
 (buffers 856 11))