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]
merge revision(s) 59056: [Backport #13648] [Backport #13699]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_4@59363 b2dd03c8-39d4-4d8f-98ff-823fe69b080e