Core/Creature: Fall back to combat list if calling for help without threat list

Port From (https://github.com/TrinityCore/TrinityCore/commit/6a91fe3fbe28e3bf36ab6107b9c6cbb842f65262)

Source/Game/Combat/CombatManager.cs

@@ -88,7 +88,7 @@ namespace Game.Combat
             return false;
         }
 
-        Unit GetAnyTarget()
+        public Unit GetAnyTarget()
         {
             if (!_pveRefs.Empty())
                 return _pveRefs.First().Value.GetOther(_owner);

Source/Game/Entities/Creature/Creature.cs

@@ -2182,6 +2182,8 @@ namespace Game.Entities
             Unit target = GetThreatManager().GetCurrentVictim();
             if (target == null)
                 target = GetThreatManager().GetAnyTarget();
+            if (target == null)
+                target = GetCombatManager().GetAnyTarget();
             Cypher.Assert(target != null, $"Creature {GetEntry()} ({GetName()}) is engaged without threat list");
 
             var u_do = new CallOfHelpCreatureInRangeDo(this, target, radius);