label-mode (Vim 7.4.791 or older): 'spellfile' not restored

[jhrmnn]

Current vim-sneak and Neovim 0.2.0.

To reproduce:

testrc.vim:

filetype off
call plug#begin('~/.local/share/nvim/plugged')
Plug 'justinmk/vim-sneak'
call plug#end()
filetype plugin indent on
let g:sneak#label = 1

echo 'test test test' | vim -u testrc.vim -

:set spellfile=.utf-8.add 
sst
:set spellfile?

Note it doesn't happen with only one or two "test".

Possibly related to #110.

[justinmk]

FWIW this shouldn't happen with Vim 7.4.792 or Nvim 0.2 since c2cbcf7

But it still needs to be fixed for older versions.