iseq.c: potential memory leak

* iseq.c (iseq_load): keep type_map to get rid of memory leak.
  based on a patch by Eric Wong at [ruby-core:59699].  [Bug #9399]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44568 b2dd03c8-39d4-4d8f-98ff-823fe69b080e