bug#24355: 25.1; Block name sometimes not commented out in conf-mode

[Alex]

Recipe:

1. emacs -Q
2. Enter new buffer
3. Type the following:
#name { block }

#name { block
#}

4. M-x conf-mode

The first line has 'name' commented out correctly while line
3 still has 'name' (and the beginning #) in the 'font-lock-type-face'.

This also happens in conf-mode types other than Unix which use different
comment characters (such as Xdefaults and Windows).


In GNU Emacs 25.1.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.20.7)
 of 2016-08-21 built on lylat
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
System Description:     Debian GNU/Linux testing (stretch)

Important settings:
  value of $LC_CTYPE: en_CA.utf8
  value of $LANG: en_CA.utf8
  locale-coding-system: utf-8-unix

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

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