Fix SOC/CS slots ordering support (#382, #392)

In SOC and CS slots start from -1.
e.g. knife slot is 0 in SOC/CS and 1 in COP.

res/gamedata/configs/openxray.ltx

@@ -35,3 +35,7 @@ game_mode = cop
 ; Always try to put item in the slot, SOC behaviour
 ; For the comparison, COP tries to do that only if item has default_to_ruck = false
 default_to_slot = false
+
+; SOC/CS slots ordering
+; e.g. knife slot is 0 in SOC/CS and 1 in COP
+minus_one_slot_ordering = false

src/xrGame/script_game_object_inventory_owner.cpp

@@ -1258,6 +1258,9 @@ CScriptGameObject* CScriptGameObject::item_in_slot(u32 slot_id) const
         return (0);
     }
 
+    if (pSettingsOpenXRay->read_if_exists<bool>("compatibility", "minus_one_slot_ordering", ShadowOfChernobylMode || ClearSkyMode))
+        ++slot_id;
+
     CInventoryItem* result = inventory_owner->inventory().ItemFromSlot((u16)slot_id);
     return (result ? result->object().lua_game_object() : 0);
 }