Summary:
TaskGroupingProxyModel used to return QVariant() as the
AbstractTasksModel::VirtualDesktop role for task groups,
resulting in TasksModel to sort task groups indiscrimi-
nately at the front of the list. In this patch, it instead
returns the lowest virtual desktop found among the children.
BUG:384747
Reviewers: #plasma
Subscribers: plasma-devel
Tags: #plasma
Differential Revision: https://phabricator.kde.org/D11257