Reads with max_slave_connections=0 after a switchover do not discard stale connections

If readwritesplit is configured with max_slave_connections=0 and a switchover happens, reads will still use the old master server even if the new master would be available. When the next write occurs, the master is replaced and the stale connection is discarded. The expected behavior with max_slave_connections=0 is that as soon as the staleness of the master is detected, the connection should be discarded. If no replacement is available, the read should not proceed even if a connection to a server with the Slave status would be available.