fixed npe in Session

wizard-client/wizard-client-libgdx/core/src/main/java/eu/jonahbauer/wizard/client/libgdx/state/Session.java

@@ -62,22 +62,23 @@ public final class Session extends BaseState {
             var player = join.getPlayer();
             log.info("Player {} joined the session.", player.getName());
             players.put(player.getUuid(), player);
-            sessionScreen.addPlayer(player);
+            if (sessionScreen != null) sessionScreen.addPlayer(player);
             return Optional.empty();
         } else if (message instanceof PlayerLeftMessage leave) {
             var uuid = leave.getPlayer();
             var player = players.remove(uuid);
             log.info("Player {} left the session.", player.getName());
-            sessionScreen.removePlayer(uuid);
+            if (sessionScreen != null) sessionScreen.removePlayer(uuid);
             return Optional.empty();
         } else if (message instanceof PlayerModifiedMessage modified) {
             var player = modified.getPlayer();
             log.info("Player {} was modified.", player.getName());
             players.put(player.getUuid(), player);
-            sessionScreen.modifyPlayer(player);
-
-            if (self.equals(player.getUuid())) {
-                sessionScreen.setReady(player.isReady());
+            if (sessionScreen != null) {
+                sessionScreen.modifyPlayer(player);
+                if (self.equals(player.getUuid())) {
+                    sessionScreen.setReady(player.isReady());
+                }
             }
 
             return Optional.empty();
@@ -89,11 +90,11 @@ public final class Session extends BaseState {
             // TODO display error
             log.error(nack.getMessage());
             sending = false;
-            sessionScreen.setSending(false);
+            if (sessionScreen != null) sessionScreen.setSending(false);
             return Optional.empty();
         } else if (sending && message instanceof AckMessage) {
             sending = false;
-            sessionScreen.setSending(false);
+            if (sessionScreen != null) sessionScreen.setSending(false);
             return Optional.empty();
         } else {
             return unexpectedMessage(client, message);
@@ -105,7 +106,7 @@ public final class Session extends BaseState {
             log.warn("Please slow down");
         } else {
             sending = true;
-            sessionScreen.setSending(true);
+            if (sessionScreen != null) sessionScreen.setSending(true);
             client.send(new ReadyMessage(ready));
         }
         return Optional.empty();
@@ -127,6 +128,7 @@ public final class Session extends BaseState {
         sessionScreen.setReady(players.get(self).isReady());
         sessionScreen.setPlayerName(getName());
         sessionScreen.setSession(session, sessionName, configuration);
+        sessionScreen.setSending(sending);
         return Optional.empty();
     }