Date overflow error in scheduler journal client for some visit type

Another instance of [1] with a more recent version of the scheduler.

After deploying the swh.scheduler v0.20, this error got raised by the monitoring and sentry [2].

swhscheduler@saatchi:~$ /usr/bin/swh scheduler --config-file /etc/softwareheritage/scheduler/journal-client.yml journal-client
Traceback (most recent call last):
  File "/usr/bin/swh", line 11, in <module>
    load_entry_point('swh.core==0.15.0', 'console_scripts', 'swh')()
  File "/usr/lib/python3/dist-packages/swh/core/cli/__init__.py", line 185, in main
    return swh(auto_envvar_prefix="SWH")
  File "/usr/lib/python3/dist-packages/click/core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/usr/lib/python3/dist-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/lib/python3/dist-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/lib/python3/dist-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/lib/python3/dist-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/usr/lib/python3/dist-packages/swh/scheduler/cli/journal.py", line 52, in visit_stats_journal_client
    nb_messages = client.process(worker_fn)
  File "/usr/lib/python3/dist-packages/swh/journal/client.py", line 265, in process
    batch_processed, at_eof = self.handle_messages(messages, worker_fn)
  File "/usr/lib/python3/dist-packages/swh/journal/client.py", line 292, in handle_messages
    worker_fn(dict(objects))
  File "/usr/lib/python3/dist-packages/swh/scheduler/journal_client.py", line 274, in process_journal_objects
    queue_position_per_visit_type, visit_stats_d
  File "/usr/lib/python3/dist-packages/swh/scheduler/journal_client.py", line 101, in next_visit_queue_position
    return current_position + visit_interval
OverflowError: date value out of range

Migrated from T3748 (view on Phabricator)