bug#27422: 25.2; Desktop mode fails to restore window registers

[Pierre Neidhardt <ambrevar@gmail.com>]

Steps to reproduce:

	$ emacs -Q -f desktop-save-mode
	C-x r w a
	C-x C-c
	y <RET>
	$ emacs -Q -f desktop-read
	C-x r j

The last command returns the error:
> user-error: Register doesn’t contain a buffer position or configuration

	M-x list-registers

shows in buffer:

> Register a contains a rectangle starting with Unprintable entity

This is mentioned in #17090.

Also Stefan Monnier wrote in
https://groups.google.com/forum/#!topic/gnu.emacs.help/64aO_O43530:

> This said, I have the impression that this is already done (at least partly)
> in newer Emacsen.

Don't know what it's worth.



In GNU Emacs 25.2.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.22.10)
 of 2017-04-22 built on juergen
Windowing system distributor 'The X.Org Foundation', version 11.0.11903000
System Description:	Arch Linux

Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --with-x-toolkit=gtk3 --with-xft --with-modules
 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe
 -fstack-protector-strong' 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 GCONF GSETTINGS
NOTIFY ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 MODULES

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