Bug: Socket leak if hostname resolution fails in DdpClient constructor

[travisbreaks]

Hey! Was looking through the code and noticed a potential resource leak in the DdpClient constructor.

The Issue

If InetAddress.getByName(hostname) throws UnknownHostException, the DatagramSocket created on the previous line never gets closed:

this.socket = new DatagramSocket();              // socket created
this.targetAddress = InetAddress.getByName(hostname);  // if this throws...
// socket is leaked

Suggested Fix

Wrap the constructor in a try-catch that cleans up on failure:

DatagramSocket sock = null;
try {
    sock = new DatagramSocket();
    this.targetAddress = InetAddress.getByName(hostname);
    this.socket = sock;
    this.sendPacket = new DatagramPacket(new byte[0], 0, 0, targetAddress, port);
} catch (SocketException e) {
    throw new DdpException("Failed to create UDP socket", e);
} catch (UnknownHostException e) {
    if (sock != null) sock.close();
    throw new DdpException("Invalid hostname: " + hostname, e);
}

Also worth considering: implementing AutoCloseable so consumers can use try-with-resources:

public class DdpClient implements AutoCloseable {
    // existing close() method already works
}

Not urgent since this only triggers on bad hostnames, but good to tighten up before a wider release.