fix: add null check and clean up empty dirty chunks

Author: Mapacheee

src/main/java/me/mapacheee/extendedhorizons/chunk/FakeChunkService.java

@@ -275,7 +275,11 @@ public void handleRealChunkInteraction(World world, int chunkX, int chunkZ) {
             addFakeChunkSubscription(playerId, worldId, chunkKey);
         }
 
-        if (targets.isEmpty()) return;
+        if (targets.isEmpty()) {
+            dirtyFakeChunks.remove(key);
+            return;
+        }
+        
         for (UUID playerId : targets) {
             Player player = Bukkit.getPlayer(playerId);
             if (player == null || !player.isOnline()) {

src/main/java/me/mapacheee/extendedhorizons/chunk/listener/PlayerChunkListener.java

@@ -40,6 +40,7 @@ public void onQuit(PlayerQuitEvent event) {
 
     @EventHandler
     public void onMove(PlayerMoveEvent event) {
+        if (event.getTo() == null || event.getFrom() == null) return;
         if (event.getTo().getChunk().equals(event.getFrom().getChunk())) return;
         fakeChunkService.handleMove(event.getPlayer());
     }