Running an arbitrary command panics

Running an arbitrary command (e.g.: `firefox --no-remote`) panics:

```console
$ yofi
[type `firefox --no-remote` and hit enter]
thread 'main' panicked at 'Internal error: selected_item overflow', src/state.rs:28:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```