fix(membership): Return the local join error when there are no remote servers to try

changelog.d/+local-join-forbidden.bugfix.md

@@ -0,0 +1 @@
+Joining a local room the user is not allowed to join now returns `403 M_FORBIDDEN` instead of `500 M_UNKNOWN` when there are no other servers to try.

src/service/rooms/membership/mod.rs

@@ -221,6 +221,9 @@ impl Service {
 					// We couldn't authorize a local join, probably because it's
 					// restricted and we couldn't satisfy
 					// the join rules ourselves.
+					if servers.is_empty() {
+						return Err(err);
+					}
 					info!(?err, "Failed to join room locally, trying over federation instead");
 				},
 			}