xwayland: Avoid terminating kwin process if a critical error has occurred with Xwayland
Currently, the Xwayland server may emit the criticalError() signal. When it's emitted, the application object will call exit() (boo!).
We don't really want to call exit() when kwin fails to start the Xwayland server. For example, imagine that the user has removed the xwayland package on purpose and later on kwin attempts to restart the server due to a crash. In that case, we don't want to bring down the entire session!
In addition to that, since we want kwin to survive Xwayland crashes, printing "FATAL ERROR" is highly undesirable.
Edited by Vlad Zahorodnii