bug#25008: 26.0.50; hack-local-variables error

[Mark Oteiza <mvoteiza@udel.edu>]

From -Q:

1. C-x b *foobar*
2. Insert

  # foobar -*- conf -*-

3. M-: (hack-local-variables)

Debugger entered--Lisp error: (wrong-type-argument listp conf-mode)
  hack-local-variables-filter(conf-mode nil)
  hack-local-variables()
  eval((hack-local-variables) nil)
  eval-expression((hack-local-variables) nil)
  funcall-interactively(eval-expression (hack-local-variables) nil)
  call-interactively(eval-expression nil nil)
  command-execute(eval-expression)

I suspect it has to do with
http://git.savannah.gnu.org/cgit/emacs.git/commit/?id=4a80c8bb276d

In GNU Emacs 26.0.50.1 (x86_64-unknown-linux-gnu, X toolkit, Xaw scroll bars)
 of 2016-11-22 built on logos
Repository revision: c542fab20f53374dd0c71dce949ef370fc76fa48

Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --without-gconf --with-modules
 --with-x-toolkit=lucid 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe
 -fstack-protector-strong --param=ssp-buffer-size=4 -g
 -fvar-tracking-assignments -g -fvar-tracking-assignments'
 CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
LUCID X11 MODULES LIBSYSTEMD