fix(userbot): encode absent pyrogram raw payloads as empty json

backend/src/userbot/handlers/raw/read_receipts.py

@@ -3,6 +3,7 @@ from datetime import UTC, datetime
 from pyrogram import raw, utils
 
 from userbot import PyroClient
+from userbot.modules.raw_json import raw_json
 from userbot.modules.read_receipts import repository
 from utils.events import notify_bg_event
 
@@ -23,7 +24,7 @@ async def handle(
         chat_id,
         datetime.now(UTC),
         update.max_id,
-        str(update),
+        raw_json(update),
     )
     await notify_bg_event(
         ctx.pool, "receipt", ctx.account_id, chat_id=chat_id, message_id=update.max_id