Discard known packs if we don't have a target

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

@@ -170,7 +170,11 @@ public class ClientConfigSessionHandler implements MinecraftSessionHandler {
   @Override
   public boolean handle(KnownPacksPacket packet) {
     callConfigurationEvent().thenRun(() -> {
-      player.getConnectionInFlightOrConnectedServer().ensureConnected().write(packet);
+      VelocityServerConnection targetServer =
+          player.getConnectionInFlightOrConnectedServer();
+      if (targetServer != null) {
+        targetServer.ensureConnected().write(packet);
+      }
     }).exceptionally(ex -> {
       logger.error("Error forwarding known packs response to backend:", ex);
       return null;