need to restore previous value. [ruby-talk:77577]

* array.c (rb_ary_fill): array length may be changed during the
  block execution. [ruby-talk:77579]

* array.c (rb_ary_zip): ditto.

* array.c (rb_ary_fill): ditto.

* hash.c (env_reject_bang): length may be changed during the block
  execution.

* hash.c (env_clear): ditto.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@4254 b2dd03c8-39d4-4d8f-98ff-823fe69b080e