There is a bug in pool when connection cannot be established at pool start

**Describe the bug**

There is a bug in pool when connection cannot be established at pool start.
This bug will bite when you wish close the connection

**To Reproduce**

Steps to reproduce the behavior:

1. Start your deno server
2. Start your pool
3. Try to connect
4. Exception happen (good)
5. **Start database**
6. Try to connect
7. Do insert (OK, commited)
8. **Release pool client**, then
8.5. **Exception happens.**
9. **_but query succeeds_**

**Expected behavior**

No exception

**This bug is not observed when database connection is ready at start**