iseq.c: refactoring rb_iseq_free
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63403 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
iseq.c: refactoring rb_iseq_free
not NULL too, as the function accesses the body.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63403 b2dd03c8-39d4-4d8f-98ff-823fe69b080e