Check horse entity validity in container interactions (#2584)

Fixes #2580

Spigot-Server-Patches/0419-Fix-MC-161754.patch

@@ -0,0 +1,26 @@
+From bd880ec25fa3db73d596f3307f8b36dc5eb8f701 Mon Sep 17 00:00:00 2001
+From: Spottedleaf <Spottedleaf@users.noreply.github.com>
+Date: Tue, 24 Sep 2019 16:03:00 -0700
+Subject: [PATCH] Fix MC-161754
+
+Fixes https://github.com/PaperMC/Paper/issues/2580
+
+We can use an entity valid check since this method is invoked for
+each inventory iteraction (thanks to CB) and on player tick (vanilla).
+
+diff --git a/src/main/java/net/minecraft/server/ContainerHorse.java b/src/main/java/net/minecraft/server/ContainerHorse.java
+index d1b9482d6..ad4e0a45c 100644
+--- a/src/main/java/net/minecraft/server/ContainerHorse.java
++++ b/src/main/java/net/minecraft/server/ContainerHorse.java
+@@ -76,7 +76,7 @@ public class ContainerHorse extends Container {
+ 
+     @Override
+     public boolean canUse(EntityHuman entityhuman) {
+-        return this.c.a(entityhuman) && this.d.isAlive() && this.d.g((Entity) entityhuman) < 8.0F;
++        return this.c.a(entityhuman) && (this.d.isAlive() && this.d.valid) && this.d.g((Entity) entityhuman) < 8.0F; // Paper - Fix MC-161754
+     }
+ 
+     @Override
+-- 
+2.22.1
+