Fix hidden properties to ignore [[Extensible]].

Fix hidden properties to ignore [[Extensible]].

The [[Extensible]] property prevented the very first hidden property
from being added. If any hidden property was added to the object before
preventing extension, adding subsequent hidden properties would have
succeed however.

R=svenpanne@chromium.org
BUG=v8:2034
TEST=mjsunit/regress/regress-2034

Review URL: https://chromiumcodereview.appspot.com/9844025

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11202 ce2b1a6d-e550-0410-aec6-3dcde31c8c00