(rooms): Restore permission on guild rejoin.

Restore rented owner and member permissions on rejoin.
Adds a `userid` index to `rented_members_users`.

data/migration/v3-v4/migration.sql

@@ -4,4 +4,6 @@ ALTER TABLE guild_config
   ADD COLUMN returning_message TEXT,
   ADD COLUMN starting_funds INTEGER;
 
+CREATE INDEX rented_members_users ON rented_members (userid);
+
 INSERT INTO VersionHistory (version, author) VALUES (4, 'v3-v4 Migration');