Fix bug with nil file resource for logfile.

This bug was introduced because Chef now checks that file resource
names are not nil.

See: https://github.com/opscode/chef/commit/b4c8facbf495423950345937ab4a8d6d8792ad16#diff-777c3a72344547b365dc6149ec4ebaffR111
Merge pull request #103 from chrismoos/fix_logfile_resource

Fix bug with nil file resource for logfile.