From 772088727433f67690980d516d25143c030706c1 Mon Sep 17 00:00:00 2001
From: Yamagi Burmeister <yamagi@yamagi.org>
Date: Fri, 30 Dec 2016 10:23:32 +0100
Subject: [PATCH] Make sure that a monsters enemy is still alive when deciding
 to attack.

When the monster was already killed by another monster or a coop player
some references may be NULL and the game was crashed. This was observed
by maraakte, who reported it in issue #164. I've just merged his fix
from q2dos.
---
 src/g_ai.c | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/src/g_ai.c b/src/g_ai.c
index 00b7063..cf3ef42 100644
--- a/src/g_ai.c
+++ b/src/g_ai.c
@@ -473,7 +473,11 @@ HuntTarget(edict_t *self)
 		self->monsterinfo.run(self);
 	}
 
-	VectorSubtract(self->enemy->s.origin, self->s.origin, vec);
+	if(visible(self, self->enemy))
+	{
+		VectorSubtract(self->enemy->s.origin, self->s.origin, vec);
+	}
+
 	self->ideal_yaw = vectoyaw(vec);
 
 	/* wait a while before first attack */
@@ -486,7 +490,7 @@ HuntTarget(edict_t *self)
 void
 FoundTarget(edict_t *self)
 {
-	if (!self)
+	if (!self|| !self->enemy || !self->enemy->inuse)
 	{
 		return;
 	}
@@ -824,7 +828,7 @@ M_CheckAttack(edict_t *self)
 	float chance;
 	trace_t tr;
 
-	if (!self)
+	if (!self || !self->enemy || !self->enemy->inuse)
 	{
 		return false;
 	}
@@ -1158,8 +1162,10 @@ ai_checkattack(edict_t *self, float dist)
 	qboolean hesDeadJim;
 	qboolean retval;
 
-	if (!self)
+	if (!self || !self->enemy || !self->enemy->inuse)
 	{
+		enemy_vis = false;
+
 		return false;
 	}
 
@@ -1300,10 +1306,14 @@ ai_checkattack(edict_t *self, float dist)
 		}
 	}
 
-	enemy_infront = infront(self, self->enemy);
-	enemy_range = range(self, self->enemy);
-	VectorSubtract(self->enemy->s.origin, self->s.origin, temp);
-	enemy_yaw = vectoyaw(temp);
+	if (self->enemy)
+	{
+		enemy_infront = infront(self, self->enemy);
+		enemy_range = range(self, self->enemy);
+		VectorSubtract(self->enemy->s.origin, self->s.origin, temp);
+		enemy_yaw = vectoyaw(temp);
+	}
+
 	retval = self->monsterinfo.checkattack(self);
 
 	if (retval)
@@ -1360,7 +1370,7 @@ ai_run(edict_t *self, float dist)
 	qboolean gotcha = false;
 	edict_t *realEnemy;
 
-	if (!self)
+	if (!self || !self->enemy || !self->enemy->inuse)
 	{
 		return;
 	}