mmqt hits an assert in modemdevice.cpp around here:
```
    bool success = QDBusConnection::systemBus().connect(QLatin1String(MMQT_DBUS_SERVICE),
                                         QLatin1String(MMQT_DBUS_PATH),
                                         QLatin1String(DBUS_INTERFACE_MANAGER),
                                         QStringLiteral("InterfacesAdded"),
                                         this,
                                         SLOT(onInterfacesAdded(QDBusObjectPath, ModemManager::MMVariantMapMap)));
    Q_ASSERT(success);
```

OBSERVED RESULT
mmqt assumes that modemmanager is always functional

EXPECTED RESULT
mmqt gracefully handles modemmanager failing to initialise due to e.g. hardware issues

ADDITIONAL INFORMATION
this causes downstream issues in kded and plasmashell, which causes much of the plasma session to become unfunctional due to code calling into mmqt