Handle no internet connexion

Handle correctly:

10-02 08:47:49:388 [ info nextcloud.sync.accessmanager ]:	2 "" "https://nextcloud.inrae.fr/status.php" has X-Request-ID "e9684cfd-9a58-4e54-8028-e2ebb0310342"
10-02 08:47:49:404 [ info nextcloud.sync.networkjob ]:	OCC::CheckServerJob created for "https://nextcloud.inrae.fr" + "status.php" ""
10-02 08:47:49:416 [ warning nextcloud.sync.networkjob ]:	QNetworkReply::HostNotFoundError "Host nextcloud.inrae.fr not found" QVariant(Invalid)
10-02 08:47:49:416 [ warning nextcloud.sync.networkjob.checkserver ]:	error: status.php replied  0 ""