Do not try to invoke/emit signal on shutdown.

Do not try to invoke/emit signal on shutdown.

I'm actually not sure whether this is the right way to do this,
but when the object is destroyed, we cannot delay the signal emit.
In that case, we just don't emit it at all. This is the old behavior
minus the warning:

QWARN  : tst_QWebSocketServer::tst_initialisation()
QMetaObject::invokeMethod: No such method QObject::closed()

Change-Id: I0513dd693ef7bfc43621e24361e72e90204fbea3
Reviewed-by: Kurt Pattyn <pattyn.kurt@gmail.com>