Declaring an empty global var as a reference in a function twice crashes bash

[Arthur200000]

Configuration Information:
Machine: x86_64
OS: darwin13.3.0
Compiler: gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' 
-DCONF_OSTYPE='darwin13.3.0' -DCONF_MACHTYPE='x86_64-apple-darwin13.3.0' 
-DCONF_VENDOR='apple' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL 
-DHAVE_CONFIG_H -DMACOSX   -I.  -I. -I./include -I./lib -I./lib/int\
l -I/Users/apple/Downloads/bash-4.3/lib/intl  -arch i386 -arch x86_64 -O3 
-fomit-frame-pointer -momit-leaf-frame-pointer -ffast-math -fvisibility=hidden 
-march=core2 -mtune=corei3 -mmacosx-version-min=10.8 -isysroot 
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platfo\
rm/Developer/SDKs/MacOSX10.8.sdk
uname output: Darwin Zzzzz 13.4.0 Darwin Kernel Version 13.4.0: Sun Aug 17 
19:50:11 PDT 2014; root:xnu-2422.115.4~1/RELEASE_X86_64 x86_64
Machine Type: x86_64-apple-darwin13.3.0

Bash Version: 4.3
Patch Level: 26
Release Status: release

Description:
        When you have already set a variable to empty, running `declare -gn
        varname` in a function twice crash bash with a Segment Fault.

        `set -xv` told me that bash would stop right when running declare.
        There is also some additional info from lldb.

        I have reproduced this on my OS X and Ubuntu 14.10 LTS amd64, 
        and a bash 4.3.30 on the same OS X machine, in another prefix.
        The LLDB output was nearly identical.
      
Repeat-By:
        Run this in bash, either as a script with she-bang or copy-paste in 
        interactive shell:
        ```Bash
        #!/bin/bash
        v=''
        a(){ declare -gn v; }
        a; a
        ```

--LLDB--
* thread #1: tid = 0x922581, 0x0000000100074371 bash`declare_internal + 3729, 
queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, 
address=0x29)
    frame #0: 0x0000000100074371 bash`declare_internal + 3729
bash`declare_internal + 3729:
-> 0x100074371:  orb    $0x10, 0x29(%r14)
   0x100074376:  movq   -0x58(%rbp), %rsi
   0x10007437a:  movl   0x28(%r14), %edx
   0x10007437e:  testb  $0x2, %dl