Room keys not stored when room doesn't yet exist

[TobiasFella]

1. A invites B to a room and sends a message
2. (in some situations) B will receive the to-device message with the key before receiving the invitation to the room, causing libquotient to not store the room key
3. Profit :)

[KitsuneRal]

Ooph...
While rebasing the per-connection E2EE code a couple of hours ago, it occurred to me that holding Megolm keys in a dictionary inside the ConnectionEncryptionData object might make the Room code less cumbersome. This is apparently the case to move those keys there and store them whether a room with a given id exists or not.