D8561: [d_ptr] Do not harsh destroy QThread

[David Edmundson]

davidedmundson added a reviewer: ivan.

REPOSITORY
  R161 KActivity Manager Service

REVISION DETAIL
  https://phabricator.kde.org/D8561

To: anthonyfieroni, #plasma, davidedmundson, ivan
Cc: plasma-devel, ZrenBot, progwolff, lesliezhai, ali-mohamed, jensreuterberg, 
abetts, sebas, apol, mart