random.c: ensure initialized

	* random.c (get_rnd, try_get_rnd): ensure initialized to get rid
	  of crash in forked processes.  [ruby-core:82100] [Bug #13753]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_4@59517 b2dd03c8-39d4-4d8f-98ff-823fe69b080e