Delete the correct item in removeDesktop
Summary:
QList::erase will move the data underneath where the iterator is
pointing, we want to delete the entry we're about to remove from the
list.
Test Plan: Relevant tests now behave better
Reviewers: KWin, broulik
Reviewed By: broulik
Subscribers: kde-frameworks-devel
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D16885