gbans is vulnerable to steamid spoofing

[sapphonie]

https://github.com/leighmacdonald/gbans/blob/master/sourcemod/scripting/gbans/ban.sp#L39-L47

Same issue with SourceBans, clients can spoof being unauth'd and be unbannable. Upcoming StAC 6.0 resolves this (StAC side, not gbans side) by doing magic with connect extension. If you'd like me to provide a native to query given a client index, let me know. Otherwise I can point you in the direction of the still beta unfinished code