[QNX] Stale QNX Screen events under load

In some cases the application cannot process the events for the event queue in QNX screen under a load and some events can be stale ie. referring to a window object that is already destroyed. This is not necessarily a fatal condition, but there are some qFatal() statements in this case which could be removed.

The related log outputs:

QQnx: failed to query window property, errno=2