Summary:
Client uses a static Xcb::Window helper. This so far didn't get
explicitly destroyed, so the application finalize cleaned it up.
To destroy the window the xcb_connection_t* is used which the
QGuiApplication already destroyed.
This change ensures that the window gets destroyed before the xcb
connection gets destroyed.
In addition an assert is added to KWin::connection() to ensure that
we still have the QGuiApplication::instance() when it's invoked.
This way we'll notice if we have more cases where we call into xcb
after the application went down.
Reviewers: #plasma
Subscribers: plasma-devel
Projects: #plasma
Differential Revision: https://phabricator.kde.org/D1573