Fix displaying of NetMetr empty sync code
According to https://gitlab.nic.cz/turris/project/-/issues/116#note_210578, we shouldn't display an empty sync code.
Self sign-up has been disabled due to increased spam activity. If you want to get access, please send an email to a project owner (preferred) or at gitlab(at)nic(dot)cz. We apologize for the inconvenience.
According to https://gitlab.nic.cz/turris/project/-/issues/116#note_210578, we shouldn't display an empty sync code.