BUG Upload: File versioning with existing files

I introduced a bug in #2921 where an uploaded file with a digit in the filename can not be versioned if a file with the same filename already exists.

Bug:
- upload test.jpg
- upload test.jpg again - versioned to test2.jpg
- upload test.jpg again - versioned to test3.jpg
- upload test3.jpg - should be test4.jpg but ...

`[User Error] Couldn't fix assets/Uploads/test3.jpg with 3 tries
Line 184 in framework/filesystem/Upload.php`

Bugfix for #3565