fix s3, not all storages have "path" attribute

When the current storage was a type that did not have a path attribute (S3BotoStorage from django_storage, for example) the bare except was swallowing the error and just returning <empty>, even though it does have an image. Image.name comes from Django so seems more reliable.
Merge pull request #5 from derek73/patch-1

fix s3, not all storages have "path" attribute