FA archiver: Fix a couple of resource leaks reported by coverity

Neither of these are of any significance, as the issue is whether a file
handle is closed before the application exits anyway.

git-svn-id: svn+ssh://serv0002.cs.diamond.ac.uk/home/subversion/repos/controls/diamond/trunk/python/fa-archiver@114377 e099a375-04f9-0310-9d5f-a741eaff62e1