OF-857: Synchronize connection/session cleanup

This patch is to prevent a stack overflow in certain exception cases
where a connection has been closed, but its corresponding session is
still present in the routing table.

src/java/org/jivesoftware/openfire/nio/NIOConnection.java

@@ -203,9 +203,10 @@ public class NIOConnection implements Connection {
     }
 
     public void close() {
-        boolean closedSuccessfully = false;
-        synchronized (this) {
-            if (!isClosed()) {
+    	synchronized(this) {
+    		if (isClosed()) {
+    			return;
+    		}
             try {
                 deliverRawText(flashClient ? "</flash:stream>" : "</stream:stream>", false);
             } catch (Exception e) {
@@ -214,14 +215,10 @@ public class NIOConnection implements Connection {
             if (session != null) {
                 session.setStatus(Session.STATUS_CLOSED);
             }
-                ioSession.close(false);
+            notifyCloseListeners(); // clean up session, etc.
             closed = true;
-                closedSuccessfully = true;
-            }
-        }
-        if (closedSuccessfully) {
-            notifyCloseListeners();
     	}
+        ioSession.close(false); // async via MINA
     }
 
     public void systemShutdown() {
@@ -248,12 +245,9 @@ public class NIOConnection implements Connection {
         session = owner;
     }
 
-    public boolean isClosed() {
-        if (session == null) {
+    public synchronized boolean isClosed() {
         return closed;
     }
-        return session.getStatus() == Session.STATUS_CLOSED;
-    }
 
     public boolean isSecure() {
         return ioSession.getFilterChain().contains(TLS_FILTER_NAME);