protocol: do not switch to unsafe sync mode for just a few blocks

src/cryptonote_protocol/cryptonote_protocol_handler.inl

@@ -308,7 +308,8 @@ namespace cryptonote
       << " [Your node is " << abs_diff << " blocks (" << ((abs_diff - diff_v2) / (24 * 60 * 60 / DIFFICULTY_TARGET_V1)) + (diff_v2 / (24 * 60 * 60 / DIFFICULTY_TARGET_V2)) << " days) "
       << (0 <= diff ? std::string("behind") : std::string("ahead"))
       << "] " << ENDL << "SYNCHRONIZATION started");
-      m_core.safesyncmode(false);
+      if (hshd.current_height >= m_core.get_current_blockchain_height() + 5) // don't switch to unsafe mode just for a few blocks
+        m_core.safesyncmode(false);
     }
     LOG_PRINT_L1("Remote blockchain height: " << hshd.current_height << ", id: " << hshd.top_id);
     context.m_state = cryptonote_connection_context::state_synchronizing;