Fix turtle lag (#1502)

Fix #1501

I just added a condition check to not start a new pathfinder goal if the turtle already has one set.

Needs more testing.

![Timings Comparison](https://i.imgur.com/p9eJQSo.png)

Spigot-Server-Patches/0381-Fix-turtle-lag.patch

@@ -0,0 +1,30 @@
+From 91dc08eca1f9c64aa2f8f712a314e2b8d57faf0f Mon Sep 17 00:00:00 2001
+From: BillyGalbreath <Blake.Galbreath@GMail.com>
+Date: Fri, 28 Sep 2018 12:27:54 -0500
+Subject: [PATCH] Fix turtle lag
+
+
+diff --git a/src/main/java/net/minecraft/server/EntityTurtle.java b/src/main/java/net/minecraft/server/EntityTurtle.java
+index 1b09f577e..b515eeb23 100644
+--- a/src/main/java/net/minecraft/server/EntityTurtle.java
++++ b/src/main/java/net/minecraft/server/EntityTurtle.java
+@@ -68,6 +68,7 @@ public class EntityTurtle extends EntityAnimal {
+         this.datawatcher.set(EntityTurtle.bI, Boolean.valueOf(flag));
+     }
+ 
++    private boolean isTravelling() { return dI(); } // Paper - OBFHELPER
+     private boolean dI() {
+         return ((Boolean) this.datawatcher.get(EntityTurtle.bJ)).booleanValue();
+     }
+@@ -633,7 +634,7 @@ public class EntityTurtle extends EntityAnimal {
+         }
+ 
+         public boolean a() {
+-            return !this.a.dH() && !this.a.dy() && this.a.isInWater();
++            return !this.a.isTravelling() && !this.a.dH() && !this.a.dy() && this.a.isInWater(); // Paper
+         }
+ 
+         public void c() {
+-- 
+2.19.0
+