Primary captures with `user_uploaded=False`, but `file:///cap`

[rebeccacremona]

Looks like this isn't happening any more, but some 35K records are mismarked:

>>> captures = Capture.objects.filter(role='primary', status='success', user_upload=False, url__icontains='file:///')
>>> captures.count()
35258
>>> captures = captures.order_by('-link__creation_timestamp')
>>> captures.first().link.creation_timestamp
datetime.datetime(2019, 1, 17, 14, 0, 53, tzinfo=<UTC>)

Investigate.