remove stale mempool txs before fetching new ones (and possibly failing)

Author: jamesdorfman

src/new_index/mempool.rs

@@ -499,6 +499,10 @@ impl Mempool {
             .chain_err(|| "failed to update mempool from daemon")?;
         let to_remove: HashSet<&Txid> = old_txids.difference(&new_txids).collect();
 
+        // 2. Remove missing transactions. Even if we are unable to download new transactions from
+        // the daemon, we still want to remove the transactions that are no longer in the mempool.
+        mempool.write().unwrap().remove(to_remove);
+
         // 2. Download the new transactions from the daemon's mempool
         let txids: Vec<&Txid> = new_txids.difference(&old_txids).collect();
         let to_add = daemon
@@ -510,8 +514,6 @@ impl Mempool {
             let mut mempool = mempool.write().unwrap();
             // Add new transactions
             mempool.add(to_add);
-            // Remove missing transactions
-            mempool.remove(to_remove);
 
             mempool
                 .count