[C] Fixing isPlayerCreated in IronGolem. Fixes BUKKIT-4543

The Issue:

The method used by CraftIronGolem to determine if it's player created is wrong.

Justification for this PR:

Well it needed to be fixed?

PR Breakdown:

Well it uses the right methode which was working in 1.5.2 (with new name of course)


JIRA Ticket:

BUKKIT-4543- https://bukkit.atlassian.net/browse/BUKKIT-4543