use Duration::ZERO when reading times out

src/modem.rs

@@ -85,7 +85,7 @@ impl<UART: serial::Uart> Iterator for RxIter<UART> {
                 },
                 Err(_) => {
                     if start.elapsed() > self.timeout {
-                        self.timeout = Duration::from_millis(0);
+                        self.timeout = Duration::ZERO;
                         break None
                     }
                     thread::sleep(Duration::from_millis(200));