Error when duplicating products with images

As reported by:
- http://www.magentocommerce.com/bug-tracking/issue?issue=14076
- http://www.magentocommerce.com/bug-tracking/issue?issue=14530

When duplicated a product with uploaded images, error "Illegal string offset 'new_file'" is thrown.

![Screen Shot 2013-03-09 at 2 56 31 PM](https://f.cloud.github.com/assets/1423851/240369/ababea80-890c-11e2-9cb6-0da01e128b6b.png)