bug#25153: ERC. Channel topic wipe by /topic command

[Pavel Korolev <mail@borodust.org>]

Typing "/topic #channel" correctly displays channel topic, but when one
types "/topic #channel " (see trailing space) this command sets topic of
the channel to "" which is not what exactly expected.
This is especially disturbing when autocomplete used, so typing "/topic
#cha" and pressing <TAB> will autoexpand it into  "/topic #channel "
which will wipe channel's topic after hitting <RET>.

In GNU Emacs 25.1.1 (x86_64-apple-darwin13.4.0, NS appkit-1265.21
Version 10.9.5 (Build 13F1911))
 of 2016-09-21 built on builder10-9.porkrind.org
Windowing system distributor 'Apple', version 10.3.1504
Configured using:
 'configure --with-ns '--enable-locallisppath=/Library/Application
 Support/Emacs/${version}/site-lisp:/Library/Application
 Support/Emacs/site-lisp' --with-modules'

Configured features:
NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS MODULES

Important settings:
  value of $LANG: ru_RU.UTF-8
  locale-coding-system: utf-8-unix

Major mode: ERC

Minor modes in effect:
  diff-auto-refine-mode: t
  erc-track-mode: t
  erc-track-minor-mode: t
  erc-spelling-mode: t
  erc-ring-mode: t
  erc-networks-mode: t
  erc-netsplit-mode: t
  erc-menu-mode: t
  erc-match-mode: t
  erc-list-mode: t
  erc-pcomplete-mode: t
  erc-button-mode: t
  erc-fill-mode: t
  erc-stamp-mode: t
  erc-autojoin-mode: t
  erc-unmorse-mode: t
  erc-irccontrols-mode: t
  erc-noncommands-mode: t
  erc-move-to-prompt-mode: t
  erc-readonly-mode: t
  global-log4slime-mode: t
  show-paren-mode: t
  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:
Complete, but not unique
Making completion list...
Complete, but not unique
Making completion list... [2 times]
Type "q" in help window to restore previous buffer.
Mark set [3 times]
next-line: End of buffer
Mark set [2 times]
Making completion list...
Quit

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rfc822 mml mml-sec epg mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail rfc2047 rfc2045 ietf-drums mail-utils eieio-opt speedbar
sb-image ezimage dframe find-func misearch multi-isearch find-dired grep
cl-indent macrostep-c subr-x cmacexp cc-mode cc-fonts cc-guess cc-menus
cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs align glsl-mode
dired morse vc-git diff-mode network-stream nsm starttls tls gnutls znc
erc-track erc-spelling flyspell ispell erc-ring erc-networks
erc-netsplit erc-menu erc-match erc-list erc-pcomplete pcomplete
erc-button erc-fill erc-stamp wid-edit erc-join erc-goodies erc
erc-backend erc-compat format-spec auth-source gnus-util mm-util
help-fns mail-prsvr password-cache slime-fancy slime-trace-dialog
slime-fontifying-fu slime-package-fu slime-references
slime-compiler-notes-tree slime-scratch slime-presentations bridge
slime-macrostep macrostep slime-mdot-fu slime-enclosing-context
slime-fuzzy slime-fancy-trace slime-fancy-inspector slime-c-p-c
slime-editing-commands slime-autodoc slime-repl slime-parse log4slime
advice cl slime compile etags xref cl-seq project eieio eieio-core
cl-macs arc-mode archive-mode noutline outline easy-mmode pp comint
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my-site-start finder-inf info slime-autoloads package epg-config seq
byte-opt gv bytecomp byte-compile cl-extra help-mode easymenu cconv
cl-loaddefs pcase cl-lib time-date mule-util cyril-util tooltip eldoc
electric uniquify ediff-hook vc-hooks lisp-float-type mwheel ns-win
ucs-normalize 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
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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 kqueue cocoa ns multi-tty
make-network-process emacs)

Memory information:
((conses 16 673759 26809)
 (symbols 48 37387 0)
 (miscs 40 824 1422)
 (strings 32 79562 12229)
 (string-bytes 1 2212700)
 (vectors 16 53873)
 (vector-slots 8 921634 24921)
 (floats 8 373 374)
 (intervals 56 35483 117)
 (buffers 976 88))


-- 
Best regards,
    Pavel Korolev