Fix max bans range check in SV_AddBanToList

Adding too many bans would write out of bounds. Found by Coverity.

code/server/sv_ccmds.c

@@ -846,7 +846,7 @@ static void SV_AddBanToList(qboolean isexception)
 		return;
 	}
 
-	if(serverBansCount > ARRAY_LEN(serverBans))
+	if(serverBansCount >= ARRAY_LEN(serverBans))
 	{
 		Com_Printf ("Error: Maximum number of bans/exceptions exceeded.\n");
 		return;