Fix dumpitem command not checking sender (#5025)

Spigot-Server-Patches/Paper-dumpitem-command.patch

@@ -51,6 +51,10 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
      }
  
 +    private void doDumpItem(CommandSender sender) {
++        if (!(sender instanceof Player)) {
++            sender.sendMessage("Only players can use this command");
++            return;
++        }
 +        ItemStack itemInHand = ((CraftPlayer) sender).getItemInHand();
 +        net.minecraft.server.ItemStack itemStack = CraftItemStack.asNMSCopy(itemInHand);
 +        NBTTagCompound tag = itemStack.getTag();