Fold closes when losing focus

[urxvtcd]

To reproduce:

1. Create two files. First is minimal.vim:

set nocompatible
au FocusLost * echo('Lost')
filetype plugin indent on
syntax on
set hidden

Then minimal.txt:

" {
" vim: foldmethod=marker foldlevel=0 foldmarker={,}
" It's a test
" }

3. Run gnvim on the two files:

gnvim minimal.txt -- -u minimal.vim

4. Open the fold with za
5. Move mouse so gnvim loses focus. The fold will close.

nvim version:

NVIM v0.8.0-dev-968-g09c6ce8c4

gnvim version:

gnvim v0.1.6-88-g6ba4737

Probably related to: https://github.com/equalsraf/neovim-qt/issues/591