Returns the player's 64-bit SteamID aka CommunityID.
-multirunenvironment, this will return
nilfor all "copies" of a player because they are not authenticated with Steam.
For bots, this will return
90071996842377216 (equivalent to
STEAM_0:0:0) for the first bot to join.
For each additional bot, the number increases by 1. So the next bot will be
STEAM_0:0:1) and so on.
no value for bots clientside.