partial solution to accept accentuated characters on windows

Summary: If filename contains accentuated characters, taglib fails to open it on windows if the QString is converted to utf8.

Test Plan: Elisa is now able to index files with simple accentuated characters like é, è

Reviewers: bruns, Windows

Reviewed By: bruns

Subscribers: vonreth, astippich, kde-frameworks-devel, Baloo

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D25622