add a chunk registration fix

World checks and the Chunk Add logic are inconsistent on how Y > 256, < 0, is treated

Keep them consistent

Spigot-Server-Patches/0173-Chunk-registration-fixes.patch

@@ -0,0 +1,25 @@
+From 13e68d27421f3691be5abae087a12fe87612a032 Mon Sep 17 00:00:00 2001
+From: Aikar <aikar@aikar.co>
+Date: Wed, 21 Sep 2016 22:54:28 -0400
+Subject: [PATCH] Chunk registration fixes
+
+World checks and the Chunk Add logic are inconsistent on how Y > 256, < 0, is treated
+
+Keep them consistent
+
+diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
+index 383eef2..b026e2b 100644
+--- a/src/main/java/net/minecraft/server/World.java
++++ b/src/main/java/net/minecraft/server/World.java
+@@ -1761,7 +1761,7 @@ public abstract class World implements IBlockAccess {
+             }
+ 
+             int k = MathHelper.floor(entity.locX / 16.0D);
+-            int l = MathHelper.floor(entity.locY / 16.0D);
++            int l = Math.min(15, Math.max(0, MathHelper.floor(entity.locY / 16.0D))); // Paper - stay consistent with chunk add/remove behavior
+             int i1 = MathHelper.floor(entity.locZ / 16.0D);
+ 
+             if (!entity.ab || entity.ac != k || entity.ad != l || entity.ae != i1) {
+-- 
+2.9.3
+