Only check for async callers, do not remove potentially used variables

Potentially resolves GH-138

Spigot-Server-Patches/Check-async-eligible-spawn-chunks-GH-159.patch

@@ -0,0 +1,19 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Zach Brown <1254957+zachbr@users.noreply.github.com>
+Date: Sun, 27 Mar 2016 20:24:05 -0500
+Subject: [PATCH] Check async, eligible spawn chunks, GH-159
+
+
+diff --git a/src/main/java/net/minecraft/server/SpawnerCreature.java b/src/main/java/net/minecraft/server/SpawnerCreature.java
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
+--- a/src/main/java/net/minecraft/server/SpawnerCreature.java
++++ b/src/main/java/net/minecraft/server/SpawnerCreature.java
+@@ -0,0 +0,0 @@ public final class SpawnerCreature {
+     // Spigot end
+ 
+     public int a(WorldServer worldserver, boolean flag, boolean flag1, boolean flag2) {
++        org.spigotmc.AsyncCatcher.catchOp("check for eligible spawn chunks"); // Paper - At least until we figure out what is calling this async
+         if (!flag && !flag1) {
+             return 0;
+         } else {
+--