Don't redact old megolm sessions

Old meaning received before message index tracking was implemented

Author: tulir

mautrix/crypto/store/asyncpg/store.py

@@ -319,7 +319,8 @@ async def redact_group_sessions(
         q = """
         UPDATE crypto_megolm_inbound_session
         SET withheld_code=$1, withheld_reason=$2, session=NULL, forwarding_chains=NULL
-        WHERE (room_id=$3 OR $3='') AND (sender_key=$4 OR $4='') AND session IS NOT NULL AND account_id=$5 AND is_scheduled=false
+        WHERE (room_id=$3 OR $3='') AND (sender_key=$4 OR $4='') AND account_id=$5
+          AND session IS NOT NULL AND is_scheduled=false AND received_at IS NOT NULL
         RETURNING session_id
         """
         rows = await self.db.fetch(