fix: Npc_IsDead now checks BodyState instead of returning false

Was a FIXME stub hardcoded to return false, preventing any dead-NPC checks from
working (e.g. Thorus couldn't recognize Mordrag as dead after being killed).

Now checks Props.BodyState == BsDead, which FightService sets when HP reaches 0.

Note: BodyState is runtime-only - a world reload will respawn the NPC alive. A
permanent death flag in SaveGame state is needed as a follow-up fix.

Author: BoroBongo

Assets/Gothic-Core/Scripts/Services/Npc/NpcAiService.cs

@@ -388,9 +388,9 @@ public void ExtAiDrawWeapon(NpcInstance npc)
 
         public bool ExtNpcIsDead(NpcInstance npcInstance)
         {
-            // FIXME - We need to implement it properly. Just fixing NPEs for now!
-            // FIXME - e.g. used for PC_Thief_AFTERTROLL_Condition() from Daedalus.
-            return false;
+            // FIXME - BodyState is runtime-only and lost on NPC reload (e.g. world reload respawns the NPC alive).
+            // A permanent death flag needs to be persisted in SaveGame state and checked here instead.
+            return npcInstance.GetUserData()?.Props.BodyState == VmGothicEnums.BodyState.BsDead;
         }
 
         public bool ExtNpcIsInState(NpcInstance npc, int state)