get_options_data() returns an empty string instead of the passed default when the option isn't set

From this point on:

    $value[ $option ] = isset( $value[ $option ] ) ? $value[ $option ] : '';

doing an `isset( $value[ $option ] )` check will always succeed, thus `get_options_data()` will just return an empty string instead of whatever is passed as `$default` when the option isn't set.