Fix manually reordering launchers.
Summary:
syncLaunchers() is called after drag operations end to write the order
of launchers in the all-capping TasksModel to the LauncherTaskModel
source model. The per-activity launcher pinning work recently broke
this by changing the model that's looped over.
Reviewers: Plasma, ivan, davidedmundson
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D4608