overlay: fix regression in pickup display

src/game/overlay.c

@@ -243,7 +243,7 @@ void __cdecl Overlay_DrawPickups(const bool timed)
     }
 }
 
-void __cdecl Overlay_AddDisplayPickup(const GAME_OBJECT_ID object_id)
+void __cdecl Overlay_AddDisplayPickup(const int16_t object_id)
 {
     if (object_id == O_SECRET_1 || object_id == O_SECRET_2
         || object_id == O_SECRET_3) {

src/game/overlay.h

@@ -11,6 +11,6 @@ void __cdecl Overlay_MakeAmmoString(char *string);
 void __cdecl Overlay_DrawAmmoInfo(void);
 void __cdecl Overlay_InitialisePickUpDisplay(void);
 void __cdecl Overlay_DrawPickups(bool pickup_state);
-void __cdecl Overlay_AddDisplayPickup(GAME_OBJECT_ID object_id);
+void __cdecl Overlay_AddDisplayPickup(int16_t object_id);
 void __cdecl Overlay_DisplayModeInfo(const char *string);
 void __cdecl Overlay_DrawModeInfo(void);