Trouble with django-inplaceedit

Hello, 

I'm using your project (very neat btw) on the same model i use another one called django inplace edit.
I'm using these in different views and when inplace edit save it's field he get the form from the model to save it. 

By doing so it calls your field which itself calls the function ```manage_files_on_disk(sender, instance, **kwargs)```.
And this function adds the new_path 'None' to the field even if the tests are not passed which create a strange icon displayed as a file in your widget.
I indented the instruction as to do it only if the tests pass.

Regards,
Alti.

ps : my text editor automatically delete trailing whitespaces on save, these are the other changes in the file.