ProxyConnectionPool closes too many idle connections when they reach their ttl

The number of idle connections should not drop below coreCachedConnections.

Steps to reproduce:

1. Set ProxyConnectionPool configuration

   maxConnections = 16
   maxCachedConnections = 4
   coreCachedConnections = 2
   timeToLive = 10000

2. Run load test with 4 concurrent connections
3. 4 connections should be established
4. Wait for 11 seconds
5. 2 connections should still be established

Result: only 1 connection is still established. This is incorrect, 2 connections should still be established.