Add missing handler for sidestake contract (to be squashed)

src/gridcoin/contract/contract.cpp

@@ -277,6 +277,7 @@ class Dispatcher
             case ContractType::SCRAPER:    return GetScraperRegistry();
             case ContractType::VOTE:       return GetPollRegistry();
             case ContractType::MRC:        return m_mrc_contract_handler;
+            case ContractType::SIDESTAKE:  return GetSideStakeRegistry();
             default:                       return m_unknown_handler;
         }
     }