Improve NFT locking (#14510)

* Update docs

* Prevent locking of the same NFT twice

* Validate item is not locked on burn

* Cover with tests

* chore

substrate/frame/nfts/src/features/create_delete_item.rs

@@ -169,6 +169,10 @@ impl<T: Config<I>, I: 'static> Pallet<T, I> {
 		with_details: impl FnOnce(&ItemDetailsFor<T, I>) -> DispatchResult,
 	) -> DispatchResult {
 		ensure!(!T::Locker::is_locked(collection, item), Error::<T, I>::ItemLocked);
+		ensure!(
+			!Self::has_system_attribute(&collection, &item, PalletAttributes::TransferDisabled)?,
+			Error::<T, I>::ItemLocked
+		);
 		let item_config = Self::get_item_config(&collection, &item)?;
 		// NOTE: if item's settings are not empty (e.g. item's metadata is locked)
 		// then we keep the config record and don't remove it

substrate/frame/nfts/src/impl_nonfungibles.rs

@@ -341,6 +341,13 @@ impl<T: Config<I>, I: 'static> Transfer<T::AccountId> for Pallet<T, I> {
 	}
 
 	fn disable_transfer(collection: &Self::CollectionId, item: &Self::ItemId) -> DispatchResult {
+		let transfer_disabled =
+			Self::has_system_attribute(&collection, &item, PalletAttributes::TransferDisabled)?;
+		// Can't lock the item twice
+		if transfer_disabled {
+			return Err(Error::<T, I>::ItemLocked.into())
+		}
+
 		<Self as Mutate<T::AccountId, ItemConfig>>::set_attribute(
 			collection,
 			item,