Error when trying to join an empty room should be more explicit (SYN-678)

[matrixbot]

Submitted by @​matthew:matrix.org It is currently {"errcode":"M_UNKNOWN","error":"No known servers"} - i am having to string match on the error message to display a more coherent one in Vector :(

(Imported from https://matrix.org/jira/browse/SYN-678)

[richvdh]

FTR, I ripped out the string matching in vector because frankly "you cannot rejoin an empty room" was worse when the room wasn't empty.

We get this error when:

• The room never existed
• The room once existed, but everybody in it has left
• You are trying to join by room id, and the room id is on a different homeserver (and the room is not yet federated to your own homeserver).
• (I think?) You are trying to join by room alias, and the alias is on an unreachable homeserver.
• Probably some other reasons

[heyakyra]

If i get this error "Failed to join room Internal server error" when trying to join a room on the same server, is this the cause? Or would the error say "No known servers" as it says in the bug