LBP2/3 spam slots/by with empty username when trying to view developer levels in certain cases

This happens when: - the user tries to follow a story level from a review - the game receives a story level from the presence server - the user selects a story level in a custom category in LBP3 - probably in some other obscure cases I haven't found yet This can be worked around by returning these levels as user levels in these cases (slot type `user` + real ID, this approach would greatly benefit from #196 being implemented); maybe actually setting a publisher username for story levels could also be helpful to catch unknown cases, although afaik having a publisher username on a developer level will make the game not spam the server, but fail to load the user anyways in such cases.