Room upgrade: new members do not have access to the previous room

### Steps to reproduce:
- Join a room which is an upgrade of a previous room
- scroll to the beginning of the timeline
- click on "Click here to see previous message" link in the create event banner

### Observed:
- Toast not implemented: "Open not joined room"

Because the user has not joined the previous room, and preview of not joined room is not supported yet on RiotX.

### Other clients behavior:
- Riot-Web correctly displays the room preview with a button "Join the discussion". Clicking on the button correctly joins the room -> OK
- Riot-iOS goes back to the room list screen and do not open the room preview -> KO
- Riot-Android does not display the banner with "Click here to see previous message" -> KO