RFC: Fix wayland backend initialisation

Summary:
Otherwise it thinks outputs couldn't be created and it leaves.
Problem is that after this fix it crashes when it actually does things with:
kwin_wayland: /home/apol/devel/frameworks/kwin/composite.cpp:646: void KWin::Compositor::aboutToSwapBuffers(): Assertion `!m_bufferSwapPending' failed.

Test Plan: As said, it proceeds correctly and crashes elsewhere

Reviewers: KWin, davidedmundson

Reviewed By: KWin, davidedmundson

Subscribers: davidedmundson, kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D19921