The problem we had was closing a glxgears through an Aurorae theme
crashed KWin inside QtQuick.

This test case simulates the sequence:
1. starts glxgears
2. wait till we have a Client for it
3. send mouse move to guessed close button position
4. send mouse press/release at that position
5. verify the window is closed
6. verify glxgears exits

With the given commit reverted this crashes, with it in place it passes.

Please note: on CI it might fail as glxgears is not yet installed. [1]
Also we cannot enforce using Aurorae from the test yet, though on
the CI system it should get picked automatically as no other deco
plugin should be installed.

[1] Sysadmin ticket already created