Import from Multisite: Uploads paths are only updated when url is also changed

[reikjarloekl]

Describe the bug
When importing from a multisite, the uploads path is only updated (e.g., from uploads/sites/n to uploads/) when the url is changed as well.

Steps to Reproduce

1. Export a site from a multisite
2. Import the site into another wordpress instance without setting old_url and/ or new_url
3. uploads paths are not updated in database

Expected behavior

Uploads paths should be updated even when url remains the same.