Added a method to check if the server is running

NodeLookupReceiver
Only use the server if it's running

src/kademlia/core/KadServer.java

@@ -349,4 +349,9 @@ public class KadServer
         }
     }
 
+    public boolean isRunning()
+    {
+        return this.isRunning;
+    }
+
 }

src/kademlia/message/NodeLookupReceiver.java

@@ -51,9 +51,12 @@ public class NodeLookupReceiver implements Receiver
         /* Respond to the NodeLookupMessage */
         Message reply = new NodeReplyMessage(this.localNode.getNode(), nodes);
 
+        if (this.server.isRunning())
+        {
             /* Let the Server send the reply */
             this.server.reply(origin, reply, comm);
         }
+    }
 
     /**
      * We don't need to do anything here