Fix method name in invoke_http_json_rpc

Previously, the method name was printed as an exmpty string because
the input string had already been moved with `std::move`.

contrib/epee/include/storages/http_abstract_invoke.h

@@ -115,7 +115,7 @@ namespace epee
       }
       if(resp_t.error.code || resp_t.error.message.size())
       {
-        LOG_ERROR("RPC call of \"" << method_name << "\" returned error: " << resp_t.error.code << ", message: " << resp_t.error.message);
+        LOG_ERROR("RPC call of \"" << req_t.method << "\" returned error: " << resp_t.error.code << ", message: " << resp_t.error.message);
         return false;
       }
       result_struct = resp_t.result;