wallet_rpc_server: error out on getting the spend key from a hot wallet

src/wallet/wallet_rpc_server.cpp

@@ -1832,7 +1832,7 @@ namespace tools
           if (m_wallet->watch_only())
           {
             er.code = WALLET_RPC_ERROR_CODE_WATCH_ONLY;
-            er.message = "The wallet is watch-only. Cannot display seed.";
+            er.message = "The wallet is watch-only. Cannot retrieve seed.";
             return false;
           }
           if (!m_wallet->is_deterministic())
@@ -1857,6 +1857,12 @@ namespace tools
       }
       else if(req.key_type.compare("spend_key") == 0)
       {
+          if (m_wallet->watch_only())
+          {
+            er.code = WALLET_RPC_ERROR_CODE_WATCH_ONLY;
+            er.message = "The wallet is watch-only. Cannot retrieve spend key.";
+            return false;
+          }
           epee::wipeable_string key = epee::to_hex::wipeable_string(m_wallet->get_account().get_keys().m_spend_secret_key);
           res.key = std::string(key.data(), key.size());
       }