Avoid again invalid geometry of internal clients

Summary:
This adds again the workaround from 1fb2eace3fbf, which got temporarily
removed by 9b922f88332f.

BUG: 386304

Test Plan: Manually

Reviewers: KWin

Subscribers: kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D21601