Error message about file_prepare_directory() use

There seems to be a bug on this line:

http://drupalcode.org/project/html_export.git/blame/9a5ea2a674a056f2fc1a...

When I do an HTML export using this module, I see a message in the webpage containing a PHP error about trying to use a boolean (which the inner file_prepare_directory() returns) as a pass by reference variable to the outer file_prepare_directory(). The code seems to work better if I just remove one of these calls. The documentation for file_prepare_directory() is here:

http://api.drupal.org/api/drupal/includes!file.inc/function/file_prepare...

While looking at the code, I should point out the nearby "create a folders" section:

http://drupalcode.org/project/html_export.git/blame/9a5ea2a674a056f2fc1a...

It is not clear why file_prepare_directory() is called twice for the same $dir parameter, but if it does need to be called twice then that might affect what is the correct fix for the nested-invocation issue I mentioned above.