SPIGOT-5534: ItemStack copy constructor can cause legacy layer to load

By: md_5 <git@md-5.net>

paper-api/src/main/java/org/bukkit/inventory/ItemStack.java

@@ -101,7 +101,9 @@ public class ItemStack implements Cloneable, ConfigurationSerializable {
         Validate.notNull(stack, "Cannot copy null stack");
         this.type = stack.getType();
         this.amount = stack.getAmount();
+        if (this.type.isLegacy()) {
             this.data = stack.getData();
+        }
         if (stack.hasItemMeta()) {
             setItemMeta0(stack.getItemMeta(), type);
         }