Do not override initializer value with default settings.

When a new user subscribes to the shop the value from the subscription form has been overridden by Spree::Chimpy::Config.subscribed_by_default value.

Setting chimpy subscribe by default value to false
    
    #/config/initializers/spree_chimpy.rb
    config.subscribed_by_default = false

Now initializing a new Spree::User model with given subscribed attributes is not respected:

    Spree::User.new(subscribed: true)
    => #<Spree::User id: nil, encrypted_password: nil, password_salt: nil, email: nil, remember_token: nil, persistence_token: nil, reset_password_token: nil, perishable_token: nil, sign_in_count: 0, failed_attempts: 0, last_request_at: nil, current_sign_in_at: nil, last_sign_in_at: nil, current_sign_in_ip: nil, last_sign_in_ip: nil, login: nil, ship_address_id: nil, bill_address_id: nil, authentication_token: nil, unlock_token: nil, locked_at: nil, reset_password_sent_at: nil, created_at: nil, updated_at: nil, spree_api_key: nil, remember_created_at: nil, subscribed: false>

The additional check just overrides the subscribed value if not set.