Server list: very low ping server intermittently shown at 9999 ping

When running a dedicated server on localhost, it's intermittently displayed with an excessive ping, can be up to 9999.
On other refreshes, the ping is OK.

This causes it to be sorted to the bottom, so a LAN player may be unable to see their friend's server.

Extremely low ping internet servers may also be affected.

Likely related to #173 (closed).

Happens in master and stable.