Readwritesplit logs wrong warning when replication lag is not available

The following message is logged if the replication lag is not measurable.

warning: (1) (My-Service) Replication lag of 'server2' is -1 seconds, which is above the configured limit 10s. 'server2' is excluded from query routing.

The correct message to log would be that the reason why the server is removed from routing is not the lag itself but the inability to measure it.