async_client: Don't assume that there are any state events.

src/async_client.rs

@@ -400,7 +400,7 @@ impl AsyncClient {
                     }
                 }
 
-                client.joined_rooms.get(&room_id).unwrap().clone()
+                client.get_or_create_room(&room_id).clone()
             };
 
             for event in &room.timeline.events {

src/base_client.rs

@@ -250,7 +250,7 @@ impl Client {
         Ok(())
     }
 
-    fn get_or_create_room(&mut self, room_id: &str) -> &mut Arc<RwLock<Room>> {
+    pub(crate) fn get_or_create_room(&mut self, room_id: &str) -> &mut Arc<RwLock<Room>> {
         #[allow(clippy::or_fun_call)]
         self.joined_rooms
             .entry(room_id.to_string())