;ranklist doesn't support multiple entries for one user in same contest

For example: `;ranklist 652 amnesiac_dusk` gives the rank list position [as follows](
https://discordapp.com/channels/555883512952258563/563101381674926082/693867454685773966).

While it can be seen there is another virtual contest entry for the same user [which can be seen here](https://discordapp.com/channels/555883512952258563/563101381674926082/693866674767527956).

This may be because standings_by_id are stored as a dictionary (one to one) between standings and IDs.
Is it a good idea to store a list for each handle? I thought this was a relatively big change, so I raised an issue first.

Start by tracing the `;ranklist` command for contest 652 and inspect how `standings_by_id` maps handles to standings. Reproduce the case with `amnesiac_dusk`, then verify that the rank list includes both virtual contest entries for the same user.

Written by the indexing model from the issue text.