bug#18364: 24.4.50; GDB Many Windows: error in process filter: Bad string format: "doesn't start with '\"'!"

[tuhdo]

To reproduce:

- Enable GDB Many Windows: (setq gdb-many-windows t)
- Find any binary and M-x gdb 
- M-x gdb-display-memory-buffer
- Enter invalild address like "abcdef"
- Error occurs and block user from entering command in gdb buffer:

error in process filter: gdb-read-memory-custom: No symbol "abcdef" in current 
context.
error in process filter: No symbol "abcdef" in current context.
error in process filter: json-read-string: Bad string format: "doesn't start 
with '\"'!"
error in process filter: Bad string format: "doesn't start with '\"'!"

- When trying to enter new command, it displays these errors:

WARNING! Discarding GDB handler with token #21

WARNING! Discarding GDB handler with token #20



In GNU Emacs 24.4.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.10.8)
 of 2014-08-11 on tuhdo-MacBookAir
Windowing system distributor `The X.Org Foundation', version 11.0.11501000
System Description:     Ubuntu 14.04.1 LTS

Configured using:
 `configure --with-x-toolkit=gtk3'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GSETTINGS NOTIFY GNUTLS
LIBXML2 FREETYPE XFT ZLIB

Important settings:
  value of $LC_CTYPE: en_US.UTF-8
  value of $LC_MONETARY: vi_VN
  value of $LC_NUMERIC: vi_VN
  value of $LC_TIME: vi_VN
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Messages

Minor modes in effect:
  gdb-many-windows: t
  tooltip-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
  buffer-read-only: t
  line-number-mode: t

Recent input:
C-x C-f c <backspace> l i <tab> <M-backspace> c o u 
r <tab> l a b 2 <tab> <tab> b o m b <tab> . c <tab> 
<return> M-x g d b <return> <return> q u i t <return> 
C-x k <return> M-: ( s t q <backspace> <backspace> 
e t q SPC g a <backspace> d b - m a n y - w i n m d 
w <backspace> <backspace> <backspace> d o w s SPC t 
) <return> M-x g d b <return> <return> b SPC m a i 
<backspace> <backspace> <backspace> <backspace> <backspace> 
M-x b <backspace> g d b - d e i <backspace> <backspace> 
i s p <tab> m e m o <tab> <return> <help-echo> <help-echo> 
<help-echo> <down-mouse-1> <mouse-1> <help-echo> a 
b c d e f <return> n <return> C-h e C-p C-p C-n C-SPC 
C-e M-w <S-down> C-g <S-down> C-g M-x e m a c s - b 
u <tab> <backspace> <backspace> <backspace> <backspace> 
<backspace> <backspace> <backspace> <backspace> r e 
p o r t - e m <tab> <return>

Recent messages:
WARNING! Discarding GDB handler with token #20

error in process filter: gdb-read-memory-custom: No symbol "abcdef" in current 
context.
error in process filter: No symbol "abcdef" in current context.
error in process filter: json-read-string: Bad string format: "doesn't start 
with '\"'!"
error in process filter: Bad string format: "doesn't start with '\"'!"
Mark set [2 times]
Quit
Mark set
Quit

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message dired format-spec
rfc822 mml mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util help-fns mail-prsvr mail-utils gdb-mi bindat json gud easy-mmode
comint ansi-color ring vc-git cc-langs cl-loaddefs cl-lib cc-mode
cc-fonts easymenu cc-guess cc-menus cc-cmds cc-styles cc-align cc-engine
cc-vars cc-defs time-date tooltip electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel x-win x-dnd tool-bar dnd fontset image regexp-opt
fringe tabulated-list newcomment lisp-mode prog-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core frame cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer 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 make-network-process gfilenotify
dynamic-setting system-font-setting font-render-setting move-toolbar gtk
x-toolkit x multi-tty emacs)

Memory information:
((conses 16 124688 6344)
 (symbols 48 21850 0)
 (miscs 40 157 146)
 (strings 32 23169 4545)
 (string-bytes 1 738033)
 (vectors 16 13864)
 (vector-slots 8 433536 5352)
 (floats 8 88 218)
 (intervals 56 463 13)
 (buffers 976 22)
 (heap 1024 47177 1016))