reject invalid invoice locking (#798)

(cherry picked from commit 645363436d)

controller/tests/invoice.rs

@@ -184,6 +184,22 @@ fn invoice_tx_impl(test_dir: &'static str) -> Result<(), libwallet::Error> {
 	)?;
 	assert_eq!(slate.state, SlateState::Invoice2);
 
+	wallet::controller::owner_single_use(
+		wallet2.clone(),
+		mask2,
+		PathBuf::from(test_dir),
+		|api, m| {
+			assert_eq!(
+				api.tx_lock_outputs(m, &slate),
+				Err(libwallet::Error::SlateState)
+			);
+			let (_, txs) = api.retrieve_txs(m, false, None, None, None)?;
+			assert_eq!(txs.len(), 1);
+			assert_eq!(txs[0].tx_type, libwallet::TxLogEntryType::TxReceived);
+			Ok(())
+		},
+	)?;
+
 	// wallet 2 finalizes and posts
 	wallet::controller::foreign_single_use(
 		wallet2.clone(),

libwallet/src/api_impl/owner.rs

@@ -830,6 +830,9 @@ where
 	K: Keychain,
 {
 	let context = w.get_private_context(keychain_mask, slate.id.as_bytes())?;
+	if slate.state == SlateState::Invoice2 && context.input_ids.is_empty() {
+		return Err(Error::SlateState);
+	}
 	let mut excess_override = None;
 
 	let mut sl = slate.clone();