[platforms/wayland] Always ack configure
Summary:
Per protocol a zero-size can be sent indicating that the client should resize
its surface to its liking. For now change the code such that it at least sends
the ack-configure back and leaves the current size untouched.
Test Plan: Compiles.
Reviewers: KWin, davidedmundson
Reviewed By: KWin, davidedmundson
Subscribers: kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D25128