fix handling of baloo starting after elisa

Summary:
if Baloo is configured inactive at elisa start and later is enabled,
fix baloo management such that we correctly query Baloo for a list of
audio files

BUG: 387437

Test Plan: manual test allow to get the music files from baloo

Reviewers: astippich, januz, aspotashev

Reviewed By: astippich

Tags: #elisa

Differential Revision: https://phabricator.kde.org/D15298