tx_pool: wrap tx meta updates in a LockedTXN

src/cryptonote_core/tx_pool.cpp

@@ -859,6 +859,9 @@ namespace cryptonote
     std::unordered_set<crypto::key_image> k_images;
 
     LOG_PRINT_L2("Filling block template, median size " << median_size << ", " << m_txs_by_fee_and_receive_time.size() << " txes in the pool");
+
+    LockedTXN lock(m_blockchain);
+
     auto sorted_it = m_txs_by_fee_and_receive_time.begin();
     while (sorted_it != m_txs_by_fee_and_receive_time.end())
     {