Transliteration of files sometimes results in an empty filename

Sometimes, when uploading an image with transliteration enabled, the filename end up consisting only of the extension

Steps to reproduce:
I assume that you have transliteration installed/enabled and have a image field somewhere.

1. Rename a file to e.g. '~.png'
2. Upload the file in a image field

Drupal reports the following:

For security reasons, your upload has been renamed to png..

And the field fails with the following message:

The specified file png. could not be uploaded. Only files with the following extensions are allowed: jpg jpeg gif png txt doc xls pdf ppt pps odt ods odp.

Proposed solution:
Do not remove any characters from filename. Replace them with something safe instead. When filename only consist of disallowed characters we should still be able to upload/save the file.