Provide regression test case for bsdcat on empty compressed files
Allow empty files (after filters) in bsdcat command.

This changeset fixes an issue with empty compressed files, i.e.
files that after inflating are of size 0:  bsdcat would report
unrecognized archive format for those because the raw reader is
unable to handle files of zero length.
Merge pull request #87 from hroptatyr/fix/cat-empty-file

Allow empty files (after filters) in bsdcat command.