Return whether event already existed from event_handler.

Signed-off-by: Jason Volk <jason@zemos.net>

src/api/server/send_join.rs

@@ -208,6 +208,7 @@ async fn create_join_event(
 		.handle_incoming_pdu(&origin, room_id, &event_id, value.clone(), true)
 		.boxed()
 		.await?
+		.map(at!(0))
 		.ok_or_else(|| err!(Request(InvalidParam("Could not accept as timeline event."))))?;
 
 	drop(mutex_lock);