Surprising no-op DELETE when injecting a new room into a list

[DMRobertson]

• With a clean account, create room A.
• Request an initial sliding sync, sorting by recency and subscribing to the window [0, 1].
• Response has a single op:
  • SYNC(0, 0, roomA).
• Create a new room B.
• Response has two ops:
  • DELETE(1)
  • INSERT(0, roomB)

The delete is surprising since there isn't anything there are the time. This reminds me of #52

[kegsay]

It's also not wrong which is confusing. The reason why it exists is because server-side when you join a new room it is literally added to the end of the list, and then the position recalculated, causing a DELETE at the end of the list.