term::login() doesn't work with term::push()

[jcubic]

terminal::login() is documented but it don't work quite right.

Login only works when used in terminal option or with push(). But it should also work when called implicitly after the push().

const term = $('body').terminal({
    auth() {
        term.push(command => {
            term.echo(`protected command <white>${command}</white>`);
        }, {
            prompt: '# '
        }).login(function(username, password) {
            if (username == 'demo' && password == 'demo') {
                return '<TOKEN>';
            }
            return null;
        });
    }
}, {
    completion: true,
    prompt: '$ '
});

This doesn't work when user is already authenticated.

Steps to reproduce

1. Open repro
2. type auth and demo:demo as login and password
3. refresh the page
4. type auth

Actual behavior

The terminal is paused, when you press CTRL+D you're logged in.