unlet v:["count"] leaks memory

[ZyX-I]

To reproduce the leak it is enough to compile Vim with address sanitizing enabled (without disabling memory leak detection) and running vim -i NONE -u NONE --cmd 'unlet v:["count"]' --cmd cq (actually, any DI_FLAGS_RO variable should do, I initially found this when creating test suite for my version of b:changedtick patch).

VIM - Vi IMproved 8.0 (2016 Sep 12, compiled Feb 20 2017 23:00:21)
Included patches: 1-342
Compiled by root@zyx-desktop
Huge version with X11-Motif GUI.  Features included (+) or not (-):
+acl             +file_in_path    +mouse_sgr       +tag_old_static
+arabic          +find_in_path    -mouse_sysmouse  -tag_any_white
+autocmd         +float           +mouse_urxvt     +tcl
+balloon_eval    +folding         +mouse_xterm     +termguicolors
+browse          -footer          +multi_byte      +terminfo
++builtin_terms  +fork()          +multi_lang      +termresponse
+byte_offset     +gettext         -mzscheme        +textobjects
+channel         -hangul_input    +netbeans_intg   +timers
+cindent         +iconv           +num64           +title
+clientserver    +insert_expand   +packages        +toolbar
+clipboard       +job             +path_extra      +user_commands
+cmdline_compl   +jumplist        +perl            +vertsplit
+cmdline_hist    +keymap          +persistent_undo +virtualedit
+cmdline_info    +lambda          +postscript      +visual
+comments        +langmap         +printer         +visualextra
+conceal         +libcall         +profile         +viminfo
+cryptv          +linebreak       +python/dyn      +vreplace
+cscope          +lispindent      +python3/dyn     +wildignore
+cursorbind      +listcmds        +quickfix        +wildmenu
+cursorshape     +localmap        +reltime         +windows
+dialog_con_gui  +lua/dyn         +rightleft       +writebackup
+diff            +menu            +ruby            +X11
+digraphs        +mksession       +scrollbind      +xfontset
-dnd             +modify_fname    +signs           +xim
-ebcdic          +mouse           +smartindent     +xpm
+emacs_tags      +mouseshape      +startuptime     +xsmp_interact
+eval            +mouse_dec       +statusline      +xterm_clipboard
+ex_extra        +mouse_gpm       -sun_workshop    -xterm_save
+extra_search    -mouse_jsbterm   +syntax          
+farsi           +mouse_netterm   +tag_binary      
   system vimrc file: "$VIM/vimrc"
     user vimrc file: "$HOME/.vimrc"
 2nd user vimrc file: "~/.vim/vimrc"
      user exrc file: "$HOME/.exrc"
  system gvimrc file: "$VIM/gvimrc"
    user gvimrc file: "$HOME/.gvimrc"
2nd user gvimrc file: "~/.vim/gvimrc"
       defaults file: "$VIMRUNTIME/defaults.vim"
    system menu file: "$VIMRUNTIME/menu.vim"
  fall-back for $VIM: "/usr/share/vim"
Compilation: clang -c -I. -Iproto -DHAVE_CONFIG_H -DFEAT_GUI_MOTIF -DFUNCPROTO=15 -DNARROWPROTO    -fsanitize=address,undefined -DEXITFREE  -O0 -g -DEXITFREE  -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1       
Linking: clang   -L. -Wl,-O1 -fstack-protector -rdynamic -Wl,-export-dynamic -Wl,--no-undefined -Wl,-E   -fsanitize=address,undefined  -L/usr/local/lib -Wl,--as-needed -o vim  -lXp -lXmu -lXext -lXm -lXt -lSM -lICE -lXpm -lXt -lX11 -lXdmcp -lSM -lICE -ldl  -lm -lncurses -lelf -lnsl    -lacl -lattr -lgpm   -Wl,-E -Wl,-O1 -Wl,--as-needed  -L/usr/lib64/perl5/5.22.3/x86_64-linux/CORE -lperl -lpthread -lnsl -ldl -lm -lcrypt -lutil -lc   -ltcl8.6 -ldl -lz -lpthread -lieee -lm -lruby21 -lpthread -lgmp -ldl -lcrypt -lm  -L/usr/lib64    

[ZyX-I]

Leak log itself:

=================================================================
==6776==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 6 byte(s) in 1 object(s) allocated from:
    #0 0x4f5518 in __interceptor_malloc /var/tmp/portage/sys-devel/llvm-3.8.1-r2/work/llvm-3.8.1.src/projects/compiler-rt/lib/asan/asan_malloc_linux.cc:52
    #1 0xc31798 in lalloc /home/zyx/a.a/Proj/c/vim-upstream/src/misc2.c:942:21
    #2 0xc316e7 in alloc /home/zyx/a.a/Proj/c/vim-upstream/src/misc2.c:840:13
    #3 0x6f09ad in get_string_tv /home/zyx/a.a/Proj/c/vim-upstream/src/eval.c:4843:12
    #4 0x6ed7e2 in eval7 /home/zyx/a.a/Proj/c/vim-upstream/src/eval.c:4227:21
    #5 0x6eaa55 in eval6 /home/zyx/a.a/Proj/c/vim-upstream/src/eval.c:3966:9
    #6 0x6e8c29 in eval5 /home/zyx/a.a/Proj/c/vim-upstream/src/eval.c:3782:9
    #7 0x6e4241 in eval4 /home/zyx/a.a/Proj/c/vim-upstream/src/eval.c:3481:9
    #8 0x6e3863 in eval3 /home/zyx/a.a/Proj/c/vim-upstream/src/eval.c:3398:9
    #9 0x696b53 in eval2 /home/zyx/a.a/Proj/c/vim-upstream/src/eval.c:3330:9
    #10 0x67d772 in eval1 /home/zyx/a.a/Proj/c/vim-upstream/src/eval.c:3258:9
    #11 0x66edd3 in get_lval /home/zyx/a.a/Proj/c/vim-upstream/src/eval.c:1940:7
    #12 0x69006f in ex_unletlock /home/zyx/a.a/Proj/c/vim-upstream/src/eval.c:2700:13
    #13 0x68fda2 in ex_unlet /home/zyx/a.a/Proj/c/vim-upstream/src/eval.c:2660:5
    #14 0x882e8c in do_one_cmd /home/zyx/a.a/Proj/c/vim-upstream/src/ex_docmd.c:2981:2
    #15 0x86278d in do_cmdline /home/zyx/a.a/Proj/c/vim-upstream/src/ex_docmd.c:1120:17
    #16 0x867d45 in do_cmdline_cmd /home/zyx/a.a/Proj/c/vim-upstream/src/ex_docmd.c:720:12
    #17 0x184230c in exe_pre_commands /home/zyx/a.a/Proj/c/vim-upstream/src/main.c:2874:6
    #18 0x183f839 in vim_main2 /home/zyx/a.a/Proj/c/vim-upstream/src/main.c:436:5
    #19 0x1831eea in main /home/zyx/a.a/Proj/c/vim-upstream/src/main.c:415:12
    #20 0x7f9e613237ef in __libc_start_main (/lib64/libc.so.6+0x207ef)

SUMMARY: AddressSanitizer: 6 byte(s) leaked in 1 allocation(s).