Add a missing break on error when adding a DoH endpoint

The break on error when adding a DoH endpoint was implied but somehow
gotten missed. This commit fixes that.

lib/ns/interfacemgr.c

@@ -555,6 +555,9 @@ ns_interface_listenhttp(ns_interface_t *ifp, isc_tlsctx_t *sslctx, char **eps,
 			result = isc_nm_http_endpoint(sock, eps[i],
 						      ns__client_request, ifp,
 						      sizeof(ns_client_t));
+			if (result != ISC_R_SUCCESS) {
+				break;
+			}
 		}
 	}