Copy layer repaints to Deleted

Summary:
If a Toplevel has scheduled layer repaints, then we have to copy them
to Deleted as well. This can happen, for example, when a client loses
shadow right before it gets closed or unmapped.

Reviewers: #kwin, graesslin

Reviewed By: #kwin, graesslin

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D18786