user registration: fix late user save for when a user id is needed

src/auth/AuthGuard.ts

@@ -65,10 +65,10 @@ export default abstract class AuthGuard<P extends AuthProof<User>> {
 
             await MysqlConnectionManager.wrapTransaction(async connection => {
                 user = User.create({});
+                await user.save(connection, c => callbacks.push(c));
                 if (onRegister) {
                     (await onRegister(connection, user)).forEach(c => callbacks.push(c));
                 }
-                await user.save(connection, c => callbacks.push(c));
             });
 
             for (const callback of callbacks) {