Improve damage handling of dead entities

Manually applied because of upstream patch file issues.
Upstream 73597ed865

Spigot-Server-Patches/Improve-damage-handling-of-dead-entities.patch

@@ -0,0 +1,22 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Phoenix616 <mail@moep.tv>
+Date: Tue, 5 Mar 2019 23:57:38 -0500
+Subject: [PATCH] Improve damage handling of dead entities
+
+Manual application of 73597ed865e92dbfad404b69eb6468fb7e129ad2 until the
+upstream patch file is sorted out.
+
+diff --git a/src/main/java/net/minecraft/server/EntityLiving.java b/src/main/java/net/minecraft/server/EntityLiving.java
+index b4f21171..77ea0ec4 100644
+--- a/src/main/java/net/minecraft/server/EntityLiving.java
++++ b/src/main/java/net/minecraft/server/EntityLiving.java
+@@ -0,0 +0,0 @@ public abstract class EntityLiving extends Entity {
+             return false;
+         } else if (this.world.isClientSide) {
+             return false;
+-        } else if (this.getHealth() <= 0.0F) {
++        } else if (this.dead || this.killed || this.getHealth() <= 0.0F) { // Paper // CraftBukkit - Don't allow entities that got set to dead/killed elsewhere to get damaged and die
+             return false;
+         } else if (damagesource.p() && this.hasEffect(MobEffects.FIRE_RESISTANCE)) {
+             return false;
+--