Summary:
QAbstractProxyModel forwards hasChildren() to the source model, which
will return a wrong value for our tree-restructuring model. Current
views/proxies don't call hasChildren(), which is how this oversight
happened, but implementing it improves model hygiene - could blow up
in the future otherwise.
Reviewers: #plasma
Subscribers: plasma-devel
Tags: #plasma
Differential Revision: https://phabricator.kde.org/D1799