Account for empty files encountered during fleecing.

When an attempting to read at EOF, the "read" method returns nil, not an empty string.
When an empty file is encountered during fleecing, this causes an unlogged exception,
resulting in all glob file info not being saved.

https://bugzilla.redhat.com/show_bug.cgi?id=1160855
https://bugzilla.redhat.com/show_bug.cgi?id=1161267
https://bugzilla.redhat.com/show_bug.cgi?id=1160859
https://bugzilla.redhat.com/show_bug.cgi?id=1161266