Fix crash in KAStatsFavouritesModel
Summary:
KAStatsFavouritesModel doesn't initialise a D-pointer for the lifespan
of the KAStatsFavouritesModel, like the name implies.
It is set in initForClient.
If the activity changes before we have a client ID, there's no point
doing anything and trying to use the clientID will crash.
BUG: 386439
Test Plan: None.
Reviewers: Plasma, hein
Reviewed By: Plasma, hein
Subscribers: anthonyfieroni, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D8608