wallet2: avoid using arbitrary random values when unknown

src/wallet/wallet2.cpp

@@ -9731,11 +9731,10 @@ uint64_t wallet2::import_key_images(const std::vector<std::pair<crypto::key_imag
     {
       const transfer_details& td = m_transfers[n];
       confirmed_transfer_details pd;
-      pd.m_change = (uint64_t)-1;                             // cahnge is unknown
+      pd.m_change = (uint64_t)-1;                             // change is unknown
       pd.m_amount_in = pd.m_amount_out = td.amount();         // fee is unknown
-      std::string err;
-      pd.m_block_height = get_daemon_blockchain_height(err);  // spent block height is unknown, so hypothetically set to the highest
-      crypto::hash spent_txid = crypto::rand<crypto::hash>(); // spent txid is unknown, so hypothetically set to random
+      pd.m_block_height = 0;  // spent block height is unknown
+      const crypto::hash &spent_txid = crypto::null_hash; // spent txid is unknown
       m_confirmed_txs.insert(std::make_pair(spent_txid, pd));
     }
   }