Move invariant IndexingLevel out of the loop

Summary:
The IndexingLevel is constant, no need to fetch it on each loop
iteration.

Reviewers: Baloo, ngraham, astippich, poboiko

Reviewed By: poboiko

Subscribers: kde-frameworks-devel

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D21698