rg process spawned by :Rg is never terminated

- [x ] I have read through https://github.com/junegunn/fzf.vim/blob/master/README.md
- [x ] I have read through https://github.com/junegunn/fzf/blob/master/README-VIM.md
- [x ] I have read through the manual page of fzf (`man fzf`)
- [x ] I have searched through the existing issues

Any time I use Rg, regardless of whether I subsequently open a file or cancel it with ESC, the `rg` process continues to run indefinitely.

If I follow thesee steps:
- open the minimal vim (or neovim) as in the issue template
- `:Rg` and open a file
- `:Rg` then ESC
- `:q!` to quit vim

My activity monitor shows this:

This makes Rg unusable, as the rg process maxes out the CPU until I manually kill it.