SceneXRender::Window uses a static XRenderPicture which it didn't clean up
Summary:
Using a static XRenderPicture results in a crash on exit as for cleanup
the already destroyed xcb_connection_t* is required.
This change ensures that the static XRenderPicture gets destroyed in the
static cleanup handler for SceneXRender::Window.
CCBUG: 363251
Reviewers: Plasma
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D1733