path_to_theme cause admin/build/block broken for admin theme

Issue Summary

Hi, i found a very small bug in the module.
The function path_to_theme in the .module file (on line 69) has broken my block pages when i have enabled an administration theme.

I solve changing the function:

$css_file_complete =  path_to_theme() .'/widgets/'. $widget_dir .'/'. $css_file;

to this:

$css_file_complete = drupal_get_path('theme', variable_get('theme_default', NULL)).'/widgets/'.$widget_dir.'/'.$css_file;

and works very well!!!
If anyone encounter this problem i hope to be usefull!!!

After all, good module! ;)