"ValueError: No filename found in rlog header" when loading ssh://anoncvs@anoncvs.NetBSD.org:/cvsroot/src

https://sentry.softwareheritage.org/organizations/swh/issues/104794/?referrer=phabricator_plugin

ValueError: No filename found in rlog header
  File "swh/loader/core/loader.py", line 391, in load
    self.prepare()
  File "swh/loader/cvs/loader.py", line 502, in prepare
    self.rlog.parse_rlog(main_rlog_file)
  File "swh/loader/cvs/rlog.py", line 220, in parse_rlog
    raise ValueError("No filename found in rlog header")

Loading failure, updating to `failed` status

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Migrated from T4629 (view on Phabricator)