PlugInstall error with directory with spaces

PlugInstall doesn't work. Probably because my user folder has a space, e.g. "C:\Users\FirstName LastName".

Error persists using `call plug#begin('C:\vim\plugged')`

Could be related to #1057


------------------------------

```
:version
NVIM v0.7.2
Build type: RelWithDebInfo
LuaJIT 2.1.0-beta3
Compiled by runneradmin@fv-az276-503

Features: -acl +iconv +tui
See ":help feature-compile"

system vimrc file: "$VIM\sysinit.vim"
fall-back for $VIM: "C:/Program Files/nvim/share/nvim"

Run :checkhealth for more info
Press ENTER or type command to continue
```

- Type:
- [x] Bug
- [ ] Enhancement
- [ ] Feature Request
- [ ] Question
- OS:
- [ ] All/Other
- [ ] Linux
- [ ] OS X
- [x] Windows
- Vim:
- [ ] Terminal Vim
- [ ] GVim
- [x] Neovim