Fix #718 Prevent <clinit> of the super class being called more than once

When a sub class is initialized, if it doesn't have a <clinit> method, it will try to call the <clinit> method of the super class event if the super class has been initialized already. This leads to the <clinit> method of the super class being called more than once.

This pull request fixes the bug of this case.
Oh, thanks for reminding me :-)