enumerator.c: fix nested maps

	* enumerator.c (lazy_map_proc, lazy_grep_iter_proc): marks values
	  returned by blocks are not packed in the case of nested maps, so
	  that the result will be same as non-lazy version.  based on the
	  patch by akihikodaki (Akihiko Odaki) at [ruby-core:81638],
	  without GCC extension.  [Bug#13648]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_4@59363 b2dd03c8-39d4-4d8f-98ff-823fe69b080e