thread.c: check initialized

* ext/thread/thread.c (get_array): check instance variables are
  initialized properly.  [ruby-core:63826][Bug #10062]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47217 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-08-19

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47218 b2dd03c8-39d4-4d8f-98ff-823fe69b080e