Hostage entity index
Returns index of the entity that a hostage is following.
Hostages can theoretically follow any entity in the game, so the
returned entity index is not necessarily a client index.
This native does not work on Condition Zero, which has a different
hostage AI than other versions of Counter-Strike.
Entity index if hostage is following something, 0 otherwise
If the provided entity index is not a hostage, an error will