Correct to_dict to flat multilevel dictionaries

[sesostris]

The to_dict function fails when flattening multi-level dictionaries. For example:

from moodle.utils.helper import to_dict

user_fields = {
    "username": "myusername",
    "auth": "email",
    "password": "TopSecretPassword",
    "firstname": "Name",
    "lastname": "Surname",
    "email": "myemail@example.com",
    "idnumber": "1001",
    "customfields": [{"type": "mycustomfield", "value": "example value"}],
}

to_dict({"users": [user_fields]})

This will generate the following output:

{'users[0][username]': 'myusername',
 'users[0][auth]': 'email',
 'users[0][password]': 'TopSecretPassword',
 'users[0][firstname]': 'Name',
 'users[0][lastname]': 'Surname',
 'users[0][email]': 'myemail@example.com',
 'users[0][idnumber]': '1001',
 'users[0][customfields[0][type]]': 'mycustomfield',
 'users[0][customfields[0][value]]': 'example value'}

However, the correct output should be like this:

{'users[0][username]': 'myusername',
 'users[0][auth]': 'email',
 'users[0][password]': 'TopSecretPassword',
 'users[0][firstname]': 'Name',
 'users[0][lastname]': 'Surname',
 'users[0][email]': 'myemail@example.com',
 'users[0][idnumber]': '1001',
 'users[0][customfields][0][type]': 'mycustomfield',
 'users[0][customfields][0][value]': 'example value'}

Note the difference in the last two lines of each output.