Core/Threat: Fix a potential crash that would occur in specific edge cases of AI being a bit naughty.

(cherry picked from commit 1847555c8c)

src/server/game/Combat/CombatManager.cpp

@@ -201,7 +201,7 @@ bool CombatManager::SetInCombatWith(Unit* who)
         NotifyAICombat(_owner, who);
     if (needOtherAI)
         NotifyAICombat(who, _owner);
-    return true;
+    return IsInCombatWith(who);
 }
 
 bool CombatManager::IsInCombatWith(ObjectGuid const& guid) const

src/server/game/Combat/ThreatManager.cpp

@@ -363,6 +363,10 @@ void ThreatManager::AddThreat(Unit* target, float amount, SpellInfo const* spell
         }
     }
 
+    // ensure we're in combat (threat implies combat!)
+    if (!_owner->GetCombatManager().SetInCombatWith(target)) // if this returns false, we're not actually in combat, and thus cannot have threat!
+        return;                                              // typical causes: bad scripts trying to add threat to GMs, dead targets etc
+
     // ok, now we actually apply threat
     // check if we already have an entry - if we do, just increase threat for that entry and we're done
     auto it = _myThreatListEntries.find(target->GetGUID());
@@ -372,10 +376,6 @@ void ThreatManager::AddThreat(Unit* target, float amount, SpellInfo const* spell
         return;
     }
 
-    // otherwise, ensure we're in combat (threat implies combat!)
-    if (!_owner->GetCombatManager().SetInCombatWith(target)) // if this returns false, we're not actually in combat, and thus cannot have threat!
-        return;                                              // typical causes: bad scripts trying to add threat to GMs, dead targets etc
-
     // ok, we're now in combat - create the threat list reference and push it to the respective managers
     ThreatReference* ref = new ThreatReference(this, target, amount);
     PutThreatListRef(target->GetGUID(), ref);