taglibextractortest: Add test for files with empty metadata

Summary:
Indicates a bug in kfilemetadata delivering genre property when genre has no value.

• Copy appropiate sample files to no-meta/
• Remove tag data with picard or kid3
• Create test (of course)

Test Plan: make test

Reviewers: mgallien, Baloo, Frameworks, bruns

Reviewed By: mgallien, Baloo, bruns

Subscribers: bruns, astippich

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D12028