merge revision(s) 40102: [Backport #8234]

	* thread_pthread.c (ruby_init_stack): Avoid using uninitialized value.
	  stackaddr and size are not set if get_stack() fails.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@40386 b2dd03c8-39d4-4d8f-98ff-823fe69b080e