return AlreadyJoined when a player attempts to join a room they are already in

crates/lavina-core/src/player.rs

@@ -177,6 +177,7 @@ pub enum ClientCommand {
 
 pub enum JoinResult {
     Success(RoomInfo),
+    AlreadyJoined,
     Banned,
 }
 
@@ -388,6 +389,9 @@ impl Player {
         if self.banned_from.contains(&room_id) {
             return JoinResult::Banned;
         }
+        if self.my_rooms.contains_key(&room_id) {
+            return JoinResult::AlreadyJoined;
+        }
 
         let room = match self.rooms.get_or_create_room(room_id.clone()).await {
             Ok(room) => room,