bugfix: Return early if no non-static outputs

If there is a cooperative closure, there will only be one output to
spend, and it will be a `StaticOutput`. Since `WalletKeysManager`'s
`spend_spendable_outputs` filters out static outputs, `KeysManager`'s
`spend_spendable_outputs` gets passed an empty list of descriptors to
spend, which results in an error (with no further information provided).

src/event.rs

@@ -564,7 +564,10 @@ where
 					&Secp256k1::new(),
 				);
 				match res {
-					Ok(spending_tx) => self.wallet.broadcast_transaction(&spending_tx),
+					Ok(Some(spending_tx)) => self.wallet.broadcast_transaction(&spending_tx),
+					Ok(None) => {
+						log_info!(self.logger, "All outputs already handled");
+					}
 					Err(err) => {
 						log_error!(self.logger, "Error spending outputs: {:?}", err);
 					}

src/wallet.rs

@@ -362,19 +362,24 @@ where
 		&self, descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>,
 		change_destination_script: Script, feerate_sat_per_1000_weight: u32,
 		secp_ctx: &Secp256k1<C>,
-	) -> Result<Transaction, ()> {
+	) -> Result<Option<Transaction>, ()> {
 		let only_non_static = &descriptors
 			.iter()
 			.filter(|desc| !matches!(desc, SpendableOutputDescriptor::StaticOutput { .. }))
 			.copied()
 			.collect::<Vec<_>>();
-		self.inner.spend_spendable_outputs(
-			only_non_static,
-			outputs,
-			change_destination_script,
-			feerate_sat_per_1000_weight,
-			secp_ctx,
-		)
+		if only_non_static.is_empty() {
+			return Ok(None);
+		}
+		self.inner
+			.spend_spendable_outputs(
+				only_non_static,
+				outputs,
+				change_destination_script,
+				feerate_sat_per_1000_weight,
+				secp_ctx,
+			)
+			.map(Some)
 	}
 
 	pub fn sign_message(&self, msg: &[u8]) -> Result<String, Error> {