Merge pull request #9333 from EOSIO/state-history-log-mod

Use fc::variant() instead of 0 to be clearer that value is not available

plugins/state_history_plugin/state_history_plugin.cpp

@@ -225,7 +225,7 @@ struct state_history_plugin_impl : std::enable_shared_from_this<state_history_pl
          }
          fc_ilog(_log, "pushing result {\"head\":{\"block_num\":${head}},\"last_irreversible\":{\"block_num\":${last_irr}},\"this_block\":{\"block_num\":${this_block}}} to send queue", 
                ("head", result.head.block_num)("last_irr", result.last_irreversible.block_num)
-               ("this_block", result.this_block ? result.this_block->block_num : 0));
+               ("this_block", result.this_block ? result.this_block->block_num : fc::variant()));
          send(std::move(result));
          --current_request->max_messages_in_flight;
          need_to_send_update = current_request->start_block_num <= current &&