Fix query of StartPlasma::hasSystemdService
ListUnitByNames did not quite work as the author (me) expected. Whilst a search for "adsfasf" yeilded an empty list a well-formed name like "asdfasdf.service" would return a result to say that service was not loaded.
This means our runtime detection of xdg-autostart-generator failed.
By using ListUnitFilesByPatterns we can filter on the status in the query, meaning this code works again. We also can query the case of it being available but explicitly disabled.