implement actual items dropping

src/items/ItemStack.cpp

@@ -12,6 +12,9 @@ ItemStack::ItemStack(itemid_t item, itemcount_t count) : item(item), count(count
 void ItemStack::set(const ItemStack& item) {
     this->item = item.item;
     this->count = item.count;
+    if (count == 0) {
+        this->item = 0;
+    }
 }
 
 bool ItemStack::accepts(const ItemStack& other) const {

src/logic/scripting/lua/libinventory.cpp

@@ -32,7 +32,7 @@ static std::shared_ptr<Inventory> get_inventory(int64_t id, int arg) {
 }
 
 static void validate_slotid(int slotid, Inventory* inv) {
-    if (slotid < 0 || uint64_t(slotid) >= inv->size()) {
+    if (static_cast<size_t>(slotid) >= inv->size()) {
         throw std::runtime_error("slot index is out of range [0..inventory.size(invid)]");
     }
 }