[cassandra] webapp error: IndexError: list index out of range

Sentry Issue: SWH-WEBAPP-4NE

IndexError: list index out of range
  File "django/core/handlers/base.py", line 197, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "swh/web/browse/views/snapshot.py", line 231, in snapshot_releases_browse
    return browse_snapshot_releases(
  File "swh/web/browse/snapshot_context.py", line 1417, in browse_snapshot_releases
    next_rel = displayed_releases[-1]["branch_name"]