Fix crash when player with potion effect changes dimension

CHANGELOG.md

@@ -1,8 +1,9 @@
-Worldthreader 2.0.4 for Minecraft 1.21.4 fixes a minor thread safety issue.
+Worldthreader 2.0.4 for Minecraft 1.21.4 fixes a crash and a minor thread safety issue.
 Please report any issues you encounter to the [issue tracker of worldthreader](https://github.com/2No2Name/worldthreader/issues). As worldthreader likely comes with massive mod compatibility issues, please do not report crashes and issues to other mods' issue trackers before confirming the issue without worldthreader.
 
 ## Fixes:
 
+- Fix crash when player with potion effect changes dimension
 - Add thread-safety to iron golem, snow golem, end portal and wither block patterns used in spawning
 
 ## Known issues

src/main/java/no2/worldthreader/mixin/dimension_change/player/instance_swap/PlayerListMixin.java

@@ -33,6 +33,7 @@ public abstract class PlayerListMixin implements ServerPlayerInstanceSwapper {
         //Create the player with a null level, which is set a bit later. The constructor uses the level to adjust the spawn position etc., which is not needed when copying the player.
         //noinspection DataFlowIssue
         ServerPlayer newPlayer = new ServerPlayer(this.server, null, previousPlayer.getGameProfile(), previousPlayer.clientInformation());
+        newPlayer.setServerLevel(newLevel);
 
         newPlayer.connection = previousPlayer.connection;
         newPlayer.restoreFrom(previousPlayer, true);
@@ -51,10 +52,7 @@ public abstract class PlayerListMixin implements ServerPlayerInstanceSwapper {
             this.playersByUUID.put(newPlayer.getUUID(), newPlayer);
         }
 
-        //Loot context or so needs the minecraft server and the random instance from the level
-        newPlayer.setServerLevel(newLevel);
         newPlayer.initInventoryMenu();
-        newPlayer.setServerLevel(null);
 
         newPlayer.setHealth(newPlayer.getHealth());
 

src/main/java/no2/worldthreader/mixin/dimension_change/player/instance_swap/ServerPlayerMixin.java

@@ -100,6 +100,10 @@ private void swapPlayerWithNewInstance(TeleportTransition teleportTransition, Ca
             throw new AssertionError("Worldthreader: Ordinals of Local Capture are incorrect!");
         }
 
+        if (WorldThreadingManager.isWrongThreadForWorld(newLevel)) {
+            throw new IllegalStateException("Worldthreader: Must create new player on destination world thread!");
+        }
+
         //Swap the player with a new instance, what could go wrong?
         ServerPlayer serverPlayer = ((ServerPlayerInstanceSwapper) this.connection).worldthreader$swapRemovedPlayerWithNewCopy((ServerPlayer) (Object) this, newLevel);
         newPlayerRef.set(serverPlayer);