Exit gracefully when there is a broken pipe error

[sigmaSd]

pkexec bandwhich -r | ls

panics with

called `Result::unwrap()` on an `Err` value: Os { code: 32, kind: BrokenPipe, message: "Broken pipe" }

This pr fixes the panic

[cyqsimon]

Thanks, good catch.

Not really a chore though so I got rid of that from the title, otherwise LGTM.

[sigmaSd]

Thanks would be great if you make a new release with this

[cyqsimon]

NP will do so after #427.