wollet: include dummy spent in spent() computation

Author: RCasatta

lwk_wollet/src/cache.rs

@@ -166,12 +166,23 @@ impl Cache {
     }
 
     pub fn spent(&self) -> Result<HashSet<OutPoint>, Error> {
+        // Dummy spent outputs are outputs that are not in height map, but we have to consider them
+        // for the utxo mode.
+        let dummy_spent: Vec<OutPoint> = self
+            .all_txs
+            .iter()
+            .filter(|(_, tx)| tx.output.is_empty()) // Only dummy tx have no outputs
+            .map(|(_, tx)| tx.input.iter().map(|i| i.previous_output))
+            .flatten()
+            .collect();
+
         Ok(self
             .heights
             .keys()
             .filter_map(|txid| self.all_txs.get(txid))
             .flat_map(|tx| tx.input.iter())
             .map(|i| i.previous_output)
+            .chain(dummy_spent)
             .collect())
     }
 }