adds a check that only single ferry can happen on a deposit request g…

…asp-1652 (#858)

pallets/rolldown/src/lib.rs

@@ -525,6 +525,8 @@ pub mod pallet {
 		UninitializedChainId,
 		// Asset can be withdrawn only to sender's address
 		NontransferableToken,
+		// the deposit was already ferried
+		AlreadyFerried,
 	}
 
 	#[cfg(feature = "runtime-benchmarks")]
@@ -1843,6 +1845,11 @@ impl<T: Config> Pallet<T> {
 			return Err(Error::<T>::AlreadyExecuted);
 		}
 
+		ensure!(
+			!FerriedDeposits::<T>::contains_key((chain, deposit_hash)),
+			Error::<T>::AlreadyFerried
+		);
+
 		let amount = deposit
 			.amount
 			.checked_sub(deposit.ferryTip)