Process Chunk.addEntities before chunkLoadEvent

1.13 undesirably changed behavior here that chunk load event fired
before the entities were added to the world.

This means any plugin that spawns entities in chunk load event
causes the entities to be registered to the chunk, and then
added to the world twice.

Moves Entity Add to World to be done anytime a chunk is
registered to the Chunk Map, and ignore other calls.

Fixes #1288

Spigot-Server-Patches/0320-Process-Chunk.addEntities-before-chunkLoadEvent.patch

@@ -0,0 +1,57 @@
+From 3413007c69032fcef8ac762e61f743b5c742df67 Mon Sep 17 00:00:00 2001
+From: Aikar <aikar@aikar.co>
+Date: Sun, 29 Jul 2018 16:56:48 -0400
+Subject: [PATCH] Process Chunk.addEntities before chunkLoadEvent
+
+1.13 undesirably changed behavior here that chunk load event fired
+before the entities were added to the world.
+
+This means any plugin that spawns entities in chunk load event
+causes the entities to be registered to the chunk, and then
+added to the world twice.
+
+Moves Entity Add to World to be done anytime a chunk is
+registered to the Chunk Map, and ignore other calls.
+
+diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
+index 4e32ae7db..f0098e910 100644
+--- a/src/main/java/net/minecraft/server/Chunk.java
++++ b/src/main/java/net/minecraft/server/Chunk.java
+@@ -897,7 +897,8 @@ public class Chunk implements IChunkAccess {
+ 
+     }
+ 
+-    public void addEntities() {
++    public void addEntities() { } // Paper - do nothing if anything calls this, we call it properly during ChunkMap.put
++    public void addEntitiesToWorld() { // Paper - rename to ensure noone else calls it
+         this.j = true;
+         this.world.b(this.tileEntities.values());
+         List[] aentityslice = this.entitySlices; // Spigot
+diff --git a/src/main/java/net/minecraft/server/ChunkMap.java b/src/main/java/net/minecraft/server/ChunkMap.java
+index 5757aa80f..c6cedba96 100644
+--- a/src/main/java/net/minecraft/server/ChunkMap.java
++++ b/src/main/java/net/minecraft/server/ChunkMap.java
+@@ -31,6 +31,7 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
+                 }
+             }
+         }
++        chunk.addEntitiesToWorld(); // Paper - call before ChunkLoadEvent to maintain pre 1.13 order, otherwise CLE can manipulate the chunks entities
+ 
+         org.bukkit.Server server = chunk.world.getServer();
+         if (server != null) {
+diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
+index ece187129..4fc3c2c35 100644
+--- a/src/main/java/net/minecraft/server/World.java
++++ b/src/main/java/net/minecraft/server/World.java
+@@ -2464,7 +2464,7 @@ public abstract class World implements GeneratorAccess, IIBlockAccess, AutoClose
+         while (iterator.hasNext()) {
+             Entity entity = (Entity) iterator.next();
+ 
+-            if (entity == null) {
++            if (entity == null || entity.valid) { // Paper - if already added, skip (shouldn't happen, but safety)
+                 continue;
+             }
+             this.entityList.add(entity);
+-- 
+2.18.0
+