When a service appears right after the ListNames() call finished, but
before the QDBusPendingCallWatcher is set up, the ::serviceRegistered
signal will be queued before the ListNames() response. As a result,
the service will be ignored by DBusServiceObserver.
Switching to QDBusInterface::callWithCallback() ensures that the
result slot is queued as soon as the response arrives, thus avoiding
the race.
Credits go to Sam Edwards for identifying the problem in
https://bugs.kde.org/show_bug.cgi?id=422111#c69
BUG: 422111
FIXED-IN: 5.24.5
Jolene K
Laurent Montel
Alexander Lohnau
Konrad Materka