D8596: Fix memory leak in FolderModel::drop

[Anthony Fieroni]

anthonyfieroni added a reviewer: Plasma.

REPOSITORY
  R119 Plasma Desktop

REVISION DETAIL
  https://phabricator.kde.org/D8596

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