Core/Threat: only send periodic threat list updates while unit is engaged

src/server/game/Combat/ThreatManager.cpp

@@ -174,6 +174,8 @@ void ThreatManager::Initialize()
 
 void ThreatManager::Update(uint32 tdiff)
 {
+    if (!CanHaveThreatList() || !IsEngaged())
+        return;
     if (_updateClientTimer <= tdiff)
     {
         _updateClientTimer = CLIENT_THREAT_UPDATE_INTERVAL;