bug#2495: 23.0.91; regression in M-x flush-lines

> 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 [email protected] mailing list.

> Please describe exactly what actions triggered the bug

emacs -Q
M-< ; beginning of *scratch* buffer
M-x flush-lines RET RET

> and the precise symptoms of the bug:

Lines matching the empty regexp are not flushed.  This used to work in
older releases.

Thanks,
andreas

> 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
> /home/andreas/ext/emacs/etc/DEBUG for instructions.

In GNU Emacs 23.0.91.2 (x86_64-unknown-linux-gnu, X toolkit)
 of 2009-02-26 on tengen
configured using `configure  '--enable-debug' --enable-ltdl-convenience'

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: C
  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: de_DE.UTF-8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default-enable-multibyte-characters: t

Major mode: Group

Minor modes in effect:
  diff-auto-refine-mode: t
  shell-dirtrack-mode: t
  gnus-topic-mode: t
  gnus-undo-mode: t
  global-hi-lock-mode: t
  hi-lock-mode: t
  show-paren-mode: t
  rcirc-track-minor-mode: t
  display-time-mode: t
  savehist-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  abbrev-mode: t