Defer creation of ServiceAnnouncer until start

This adds extra complexity from the ServiceAnnouncer not always existing
but enables later flexibility in supporting binding to an emphemeral
port instead of having to preconfigure it.

Author: fishface60

src/main/java/net/rptools/maptool/server/MapToolServer.java

@@ -83,7 +83,7 @@ public enum State {
   private final AssetProducerThread assetProducerThread;
 
   private final boolean useUPnP;
-  private final ServiceAnnouncer announcer;
+  @Nullable private ServiceAnnouncer announcer;
   private Campaign campaign;
   private ServerPolicy policy;
   private HeartbeatThread heartbeatThread;
@@ -105,11 +105,6 @@ public MapToolServer(
     this.policy = new ServerPolicy(policy);
     this.playerDatabase = playerDb;
 
-    this.announcer =
-        config == null || id == null
-            ? null
-            : new ServiceAnnouncer(id, config.getPort(), AppConstants.SERVICE_GROUP);
-
     server = ConnectionFactory.getInstance().createServer(this.config);
     messageHandler = new ServerMessageHandler(this);
     this.router = new Router();
@@ -370,6 +365,7 @@ public void stop() {
 
     if (announcer != null) {
       announcer.stop();
+      announcer = null;
     }
 
     // Unregister ourselves
@@ -434,7 +430,8 @@ public void start() throws IOException {
       }
     }
 
-    if (announcer != null) {
+    if (serviceIdentifier != null && config != null) {
+      announcer = new ServiceAnnouncer(serviceIdentifier, config.getPort(), AppConstants.SERVICE_GROUP);
       announcer.start();
     }