Fix invalid client id on sourcemod ban command

[leighmacdonald]

165781 	65496.993229 	L 06/17/2024 - 00:13:58: Error log file session closed.
165782 	65496.993274 	L 06/17/2024 - 00:13:58: [SM] Exception reported: Client index 526 is invalid
165783 	65496.993296 	L 06/17/2024 - 00:13:58: [SM] Blaming: gbans.smx
165784 	65496.993319 	L 06/17/2024 - 00:13:58: [SM] Call stack trace:
165785 	65496.993330 	L 06/17/2024 - 00:13:58: [SM]   [0] GetClientAuthId
165786 	65496.993340 	L 06/17/2024 - 00:13:58: [SM]   [1] Line 65, gbans/ban.sp::ban
165787 	65496.993351 	L 06/17/2024 - 00:13:58: [SM]   [2] Line 41, gbans/ban.sp::Native_GB_BanClient
165788 	65496.993361 	L 06/17/2024 - 00:13:58: [SM]   [4] GB_BanClient
165789 	65496.993371 	L 06/17/2024 - 00:13:58: [SM]   [5] Line 405, stac/stac_stocks.sp::BanUser
165790 	65496.993382 	L 06/17/2024 - 00:13:58: [SM]   [6] Line 406, stac/stac_cvar_checks.sp::Timer_BanUser
165791 	65498.372191 	L 06/17/2024 - 00:13:59: "MAX BOX LMAOBOX<526><[U:1:1745576146]><Blue>" changed role to "sniper"