It can now be queried by RPC, so it needs to be set before
it is otherwise needed for consensus, even if no blocks had
to be added (ie, exit and restart quickly).
LOG_PRINT_GREEN("Blockchain initialized. last block: "<<m_db->height()-1<<", "<<epee::misc_utils::get_time_interval_string(timestamp_diff)<<" time ago, current difficulty: "<<get_difficulty_for_next_block(),LOG_LEVEL_0);