Release called on client which has already been released to the pool

Steps to reproduce

1. Use loopback-connector-postgresql 5.5.0 (5.4.0 does not exhibit this issue)
2. Commit a transaction with an error (ex: unique key violation)
3. Rollback the transaction

Current Behavior

Calling transaction.commit and subsequently transaction.rollback if there is a commit error results in:

The following error from pg-pool in the rollback is uncaught and crashes the server: Release called on client which has already been released to the pool

I would expect the error to be caught (perhaps in PostgreSQL.prototype.releaseConnection?) and passed along without crashing the server

从 PostgreSQL.prototype.releaseConnection 开始，使用 loopback-connector-postgresql 5.5.0 重现事务提交错误，随后执行回滚。将回滚路径与 pg-pool 的 release 行为进行比较；当 release 错误被捕获并传递出去且不会导致服务器崩溃时，即表示完成。