fix: select join with subqueries should not tamper the subquery itself

[cyjake]

Leoric tries to optimize join queries that have offset or limit by putting them into a subquery. If the subquery itself contains another Spell as subquery, such as:

Post
  .where({
    isPrivate: true,
    authorId: User.where({ stauts: 1 }),
  })
  .with('author')
  .limit(10);

will be formatted into following SQL:

SELECT posts.*, users.* 
  FROM (SELECT * FROM users WHERE is_private = 1 AND author_id IN (...) LIMIT 10);

This optimization should not tamp the subquery User.where({ status: 1 }) passed to Post.where({}.