bug#2957: 23.0.92; ucs-insert: Completion does not work correctly with Unicode Character Name Input

[Ashutosh Mehra <ashutoshmehra@gmail.com>]

Please write in English if possible, because the Emacs maintainers
usually do not have translators to read other languages for them.

Your bug report will be posted to the emacs-pretest-bug@gnu.org mailing list.

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

BUG DESCRIPTION:
When I type the following:
C-x 8 RET greek letter alpha
and press TAB, I get several choices for the greek letter alpha
variants. But I'm unable to type anything into the minibuffer (neither
SPC nor any character) -- Emacs just doesn't accept the input. If I
press RET at this point, I get the error message "ucs-insert: Not a
Unicode character code: nil".
I tried with "emacs -Q" (no init files), and I still get this
incorrect behavior.

If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
    `bt full' and `xbacktrace'.
If you would like to further debug the crash, please read the file
d:/Progs/emacs/etc/DEBUG for instructions.


In GNU Emacs 23.0.92.1 (i386-mingw-nt5.1.2600)
 of 2009-03-31 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4)'

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: ENU
  value of $XMODIFIERS: nil
  locale-coding-system: cp1252
  default-enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  tool-bar-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
M-x C-g C-x 8 <return> g r e e k SPC l e <tab> <tab>
a l p <tab> <tab> SPC SPC SPC w <tab> <tab> <backspace>
<tab> <tab> <return> M-x r e p o r t - e m <tab> <
return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Quit
Loading Unicode character names...done
Making completion list... [6 times]
ucs-insert: Not a Unicode character code: nil