bug#26682: 26.0.50; Error at startup with minibuffer-only frame

[Stefan Monnier <monnier@IRO.UMontreal.CA>]

Some recent change in `master` has introduced a regression when using my
configuration.  I can reproduce it with the recipe below:

    src/emacs -Q --eval '(setq default-frame-alist (quote ((minibuffer . only))))'

This launches Emacs but signals an error "Attempt to delete the only
frame".


        Stefan



In GNU Emacs 26.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2017-04-27 built on lechazo
Repository revision: 79c5ea9911a9aba7db0ba0e367e06507cee2fc02
Windowing system distributor 'The X.Org Foundation', version 11.0.11901000
System Description:	Debian GNU/Linux 9.0 (stretch)

Recent messages:
Entering debugger...
Continuing.
Error: (error "Unable to activate package ‘ess’.
Required package ‘julia-mode-0.3’ is unavailable")
Loading /home/monnier/src/elisp/ProofGeneral/generic/proof-site.el (source)...done
Loading /home/monnier/etc/emacs/X11.el (source)...done
Loading /home/monnier/etc/emacs/custom.el (source)...done
Source file ‘/home/monnier/src/emacs/elpa/packages/load-dir/load-dir.el’ newer than byte-compiled file
Starting new Ispell process /usr/bin/aspell with american dictionary...
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure -C --enable-checking --with-modules --enable-check-lisp-object-type
 'CFLAGS=-Wall -g3 -Og -Wno-pointer-sign'
 PKG_CONFIG_PATH=/home/monnier/lib/pkgconfig'

Configured features:
XAW3D XPM JPEG TIFF GIF PNG SOUND GPM DBUS GSETTINGS NOTIFY GNUTLS
LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS LUCID X11
MODULES

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

Major mode: Lisp Interaction

Minor modes in effect:
  outline-minor-mode: t
  flyspell-mode: t
  checkdoc-minor-mode: t
  electric-pair-mode: t
  global-reveal-mode: t
  reveal-mode: t
  auto-insert-mode: t
  savehist-mode: t
  minibuffer-electric-default-mode: t
  url-handler-mode: t
  cl-old-struct-compat-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  global-prettify-symbols-mode: t
  prettify-symbols-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
/home/monnier/src/emacs/elpa/packages/svg/svg hides /home/monnier/src/emacs/trunk/lisp/svg
/home/monnier/src/emacs/elpa/packages/landmark/landmark hides /home/monnier/src/emacs/trunk/lisp/obsolete/landmark

Features:
(shadow sort mail-extr emacsbug message subr-x puny dired dired-loaddefs
format-spec rfc822 mml mml-sec epa derived epg gnus-util rmail
rmail-loaddefs mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils noutline outline easy-mmode flyspell
ispell checkdoc thingatpt load-dir elec-pair reveal autoinsert
proof-site proof-autoloads cl pg-vars savehist minibuf-eldef disp-table
help-mode debug advice info realgud-recursive-autoloads finder-inf
url-auth package easymenu epg-config url-handlers url-parse auth-source
cl-seq eieio eieio-core cl-macs eieio-loaddefs password-cache url-vars
seq byte-opt gv bytecomp byte-compile cconv cl-loaddefs pcase cl-lib
bbdb-loaddefs time-date mule-util tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel term/x-win x-win
term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow isearch timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame cl-generic cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932
hebrew greek romanian slovak czech european ethiopic indian cyrillic
chinese composite charscript charprop case-table epa-hook jka-cmpr-hook
help simple abbrev obarray 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 dbusbind inotify dynamic-setting system-font-setting
font-render-setting x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 8 144878 7559)
 (symbols 24 23944 1)
 (miscs 20 71 182)
 (strings 16 37557 5283)
 (string-bytes 1 1279263)
 (vectors 8 19171)
 (vector-slots 4 545328 4402)
 (floats 8 68 266)
 (intervals 28 307 0)
 (buffers 520 12))