lua: inventory library

src/items/Inventory.h

@@ -14,10 +14,10 @@ class ContentLUT;
 class ContentIndices;
 
 class Inventory : Serializable {
-    uint id;
+    int64_t id;
     std::vector<ItemStack> slots;
 public:
-    Inventory(uint id, size_t size);
+    Inventory(int64_t id, size_t size);
 
     ItemStack& getSlot(size_t index);
     size_t findEmptySlot(size_t begin=0, size_t end=-1) const;
@@ -40,10 +40,14 @@ public:
 
     static void convert(dynamic::Map* data, const ContentLUT* lut);
 
-    inline uint getId() const {
+    inline int64_t getId() const {
         return id;
     }
 
+    inline bool isVirtual() const {
+        return id < 0;
+    }
+
     static const size_t npos;
 };