馃崚 applets/taskmanager: Skip querying KActivitiesStats if recentdocs is disabled
When recent document tracking is disabled, the kactivitymanagerd Stats plug-in stops recording them in the SQLite database.
However, ResultSet will still query the database. If the user's home directory is on an NFS share, this can lead to a noticeable delay when opening the task manager context menu.
For this setup, it's best to disable recent document tracking as such entirely, and skip querying the ResultSet in the first place.
It would also match user expectation to stop seeing recent documents as soon as the feature is disabled.