multiple `Ctrl-d` is required to exit when reading stdin

[e-kwsm]

revision: c6479b4

cargo run --quiet -- -n -e p
# or
cargo run --quiet -- -e ''
# or
cargo run --quiet -- -f /dev/null

Ideally these are equivalent to cat -. Here, GNU, BSD, and uutils cat’s behave in the same way.

1. foo ⏎ → prints nothing; cat, and GNU and BSD sed’s print foo
2. Ctrl+d → prints foo; cat, and GNU and BSD sed’s exit
3. another Ctrl+d → exits