Modified to avoid closing the connection if it is already

closed.  Certain race conditions can cause this to happen
during whole-server shutdown.

jme3-networking/src/main/java/com/jme3/network/base/DefaultServer.java

@@ -608,7 +608,7 @@ public class DefaultServer implements Server
             // should always already be closed through all paths that I
             // can conceive... but it doesn't hurt to be sure. 
             for( Endpoint p : channels ) {
-                if( p == null ) 
+                if( p == null || !p.isConnected() ) 
                     continue;
                 p.close();
             }