proc.c: allocate wrapper object first

* proc.c (mnew_from_me): allocate structs after allocated wrapper
  object successfully, to get rid of potential memory leak.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42963 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-09-18

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42964 b2dd03c8-39d4-4d8f-98ff-823fe69b080e