Handle empty activate_user response

[carlosmondra]

Since user moderation was created, the response from client.activate_user is empty when moderation is active. This causes an error in the __handle_token method when trying to get the token. I suggest that the __handle_token method should check if the token is present.

How to reproduce:

email = '[email protected]'

client.register_user(email = email, first = "Daniel", last = "Mondra", password = '1234')

profile_content = {
    'names': [
        {
            'first': 'Daniel',
            'last': 'Mondra',
            'username': '~Daniel_Mondra1'
        }
    ],
    'emails': [email],
    'preferredEmail': email,
    'homepage': 'https://scholar.google.de/citations?user=CAR3A2MAAAAJ'

}

client.activate_user(email, profile_content)