Don't replace entries in the tracked player map (Fixes #2102)

Spigot-Server-Patches/0037-Send-absolute-position-the-first-time-an-entity-is-s.patch

@@ -1,4 +1,4 @@
-From ca539db6550e6555be046ed3e53f541e62d76dfb Mon Sep 17 00:00:00 2001
+From 28bfe29b176f9cf6a0549258b52db485937e19b1 Mon Sep 17 00:00:00 2001
 From: Jedediah Smith <jedediah@silencegreys.com>
 Date: Wed, 2 Mar 2016 23:13:07 -0600
 Subject: [PATCH] Send absolute position the first time an entity is seen
@@ -77,7 +77,7 @@ index 315c3d9165..aaf3a54b08 100644
  
                  this.c();
 diff --git a/src/main/java/net/minecraft/server/PlayerChunkMap.java b/src/main/java/net/minecraft/server/PlayerChunkMap.java
-index 44e3340773..6c904968d7 100644
+index 44e3340773..cfc7f5a118 100644
 --- a/src/main/java/net/minecraft/server/PlayerChunkMap.java
 +++ b/src/main/java/net/minecraft/server/PlayerChunkMap.java
 @@ -1083,10 +1083,14 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
@@ -102,7 +102,7 @@ index 44e3340773..6c904968d7 100644
                      // CraftBukkit end
  
 -                    if (flag1 && this.trackedPlayers.add(entityplayer)) {
-+                    if (flag1 && this.trackedPlayerMap.put(entityplayer, true) == null) { // Paper
++                    if (flag1 && this.trackedPlayerMap.putIfAbsent(entityplayer, true) == null) { // Paper
                          this.trackerEntry.b(entityplayer);
                      }
                  } else if (this.trackedPlayers.remove(entityplayer)) {