NEXUS-6271: Make Tika recognize empty ZIP file and UT

The test renamed back to UT from IT, as it was chatty with MimeUtil2
in place but now with Tika is not and is fast.

Issue
https://issues.sonatype.org/browse/NEXUS-6271

CI
https://bamboo.zion.sonatype.com/browse/NX-OSSF74