Don't fail the doctest if /dev/tty does not exist
//! use std::os::raw::{c_void, c_int, c_uint};
//! use iocuddle::*;
//!
-//! let mut file = std::fs::File::open("/dev/tty").unwrap();
+//! let mut file = match std::fs::File::open("/dev/tty") {
+//! Err(_) => std::process::exit(0),
+//! Ok(f) => f,
+//! };
//!
//! // This is the simplist ioctl call. The request number is provided via the
//! // Ioctl::classic() constructor. This ioctl reads a C integer from the
