Make Tika recognize empty and spanning ZIP files too

As it turns out, magic differs for non-empty, empty and
spanning ZIP files. Tika recognizes only the non-empty ZIP files.

Magic for empty ZIP file is validated with hexdump:
https://gist.github.com/cstamas/6e90ae73f83c8e4a3f42

Also described on Wikipedia
http://en.wikipedia.org/wiki/Zip_(file_format)
(see sidebar with Magic Numbers)

Issue
https://issues.apache.org/jira/browse/TIKA-1241