In a nested fzf, the parent selected value is passed in the child's template binding

- [x] I have fzf 0.23.0 or above
- [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

I.e.
```bash
cat index.txt | fzf --bind "ctrl-m:execute(cat {}.txt | fzf --bind \"ctrl-m:execute(echo {} | less)\")"
```

`ctrl-m` on an item from the first `index.txt` list, and then again on the sub list. The item that is echoed is from the parent list and not from the child/sub list.

Is it possible to get the selected item from the child list in the bind template?