fix double world add bug (#2486)

Spigot-Server-Patches/0414-only-add-passanger-entities-once-from-spawners.patch

@@ -0,0 +1,22 @@
+From 269842f724c46c5faed547d65fa33619b794ccd5 Mon Sep 17 00:00:00 2001
+From: kickash32 <kickash32@gmail.com>
+Date: Wed, 21 Aug 2019 23:57:32 +0500
+Subject: [PATCH] only add passanger entities once from spawners
+
+
+diff --git a/src/main/java/net/minecraft/server/MobSpawnerAbstract.java b/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
+index b05f6c2f..a4e6be54 100644
+--- a/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
++++ b/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
+@@ -195,7 +195,7 @@ public abstract class MobSpawnerAbstract {
+     }
+ 
+     private void a(Entity entity) {
+-        if (this.a().addEntity(entity, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.SPAWNER)) { // CraftBukkit
++        if (entity.valid || this.a().addEntity(entity, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.SPAWNER)) { // CraftBukkit // Paper
+             Iterator iterator = entity.getPassengers().iterator();
+ 
+             while (iterator.hasNext()) {
+-- 
+2.22.0
+