Work around Darwn (macOS) weirdness

It seems to return a length of 16 and an all zero address for unnamed
Unix addresses.

src/sys/unix/uds/listener.rs

@@ -96,7 +96,20 @@ pub(crate) fn accept(listener: &net::UnixListener) -> io::Result<(UnixStream, So
     });
 
     let socket = socket.map(UnixStream::from_std)?;
-    let path_len = socklen as usize - path_offset(&sockaddr);
+
+    #[allow(unused_mut)] // See below.
+    let mut path_len = socklen as usize - path_offset(&sockaddr);
+    // Darwin is being weird, it return a length of 16, but other an unnamed
+    // (all zero) address. Map that to a length of 0 to match other OS.
+    #[cfg(any(
+        target_os = "ios",
+        target_os = "macos",
+        target_os = "tvos",
+        target_os = "watchos",
+    ))]
+    if socklen == 16 && sockaddr.sun_path[0] == 0 {
+        path_len = 0;
+    }
     let address = SocketAddr::from_pathname(Path::new(OsStr::from_bytes(unsafe {
         // SAFETY: going from i8 to u8 is fine in this context.
         &*(&sockaddr.sun_path[..path_len] as *const [libc::c_char] as *const [u8])