Fix inconsistency in master server listing

This patch fixes an issue with server listing where empty packets were sent to a server, interfering with it's response and blocking the SERVERINFO packet that the server replies with. I was originally under the assumption that it was harmless considering that empty packets would be ignored server-side, but it wasn't, and the server instead actually responded to it, thus responding with a bad packet and causing the server to not appear on the master server.

Here's the current behavior:

Here's what happens with this patch:

The severity of the issue is based on numerous factors though, like server state and UDP packet order, so the results are wildly inconsistent.