Small fix for public UI display of file versions

Not all URI parsable stings will have a defined scheme i.e.

/path/to/file.txt

In this case the scheme is nil so the interface will "crash".
Therefore check for the scheme as well when looking to add the
the file_uri link.
Merge pull request #77 from mark-cooper/public_file_versions_fix

Small fix for public UI display of file versions