Workaround a system icon tray issue in bug

QTimer::singleShot(time, QObject*, char*)
QTimer::singleShot(time, QObject*, PointerToFunction)

behave differently when time == 0

So the porting had an effect

This patch migrates to QMetaObject::invokeMethod which is clearer

CCBUG: 352055

There seems to be two different bug in 352055 but looks similar, the other one is fixed in Qt 5.6 according to Albert Astals Cid.