Use IItemHandler instead of IInventory internally (#2971)

* Use IItemHandler instead of IInventory internally

src/main/java/appeng/util/inv/AdaptorItemHandler.java

@@ -38,6 +38,12 @@ public class AdaptorItemHandler extends InventoryAdaptor
 		this.itemHandler = itemHandler;
 	}
 
+	@Override
+	public boolean hasSlots()
+	{
+		return itemHandler.getSlots() > 0;
+	}
+
 	@Override
 	public ItemStack removeItems( int amount, ItemStack filter, IInventoryDestination destination )
 	{