Do not print an exception if a client closed before switching to config state

Author: electronicboy

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ConnectedPlayer.java

@@ -1287,6 +1287,11 @@ private boolean sendKeepAliveToBackend(final @Nullable VelocityServerConnection
   public void switchToConfigState() {
     server.getEventManager().fire(new PlayerEnterConfigurationEvent(this, getConnectionInFlightOrConnectedServer()))
         .completeOnTimeout(null, 5, TimeUnit.SECONDS).thenRunAsync(() -> {
+          // if the connection was closed earlier, there is a risk that the player is no longer connected
+          if (!connection.getChannel().isActive()) {
+            return;
+          }
+
           if (bundleHandler.isInBundleSession()) {
             bundleHandler.toggleBundleSession();
             connection.write(BundleDelimiterPacket.INSTANCE);