🚑️ zb: Handle 0 bytes received from socket

Seems the assumpption that we can't ever get 0 bytes is wrong. Had this
in busd:

thread 'tokio-runtime-worker' panicked at 'assertion failed: read == 1', /home/zeenix/.cargo/git/checkouts/zbus-8f2422ba485129bc/662a6d1/zbus/src/handshake.rs:697:21

zbus/src/raw/socket.rs

@@ -40,6 +40,12 @@ fn fd_recvmsg(fd: RawFd, buffer: &mut [u8]) -> io::Result<(usize, Vec<OwnedFd>)>
 
     match recvmsg::<UnixAddr>(fd, &mut iov, Some(&mut cmsgspace), MsgFlags::empty()) {
         Ok(msg) => {
+            if msg.bytes == 0 {
+                return Err(io::Error::new(
+                    io::ErrorKind::UnexpectedEof,
+                    "failed to read from buffer",
+                ));
+            }
             let mut fds = vec![];
             for cmsg in msg.cmsgs() {
                 #[cfg(any(target_os = "freebsd", target_os = "dragonfly"))]