Ruby

io.c: keep fptr read-closed

• io.c (rb_io_close_read): keep fptr in write_io to be discarded, to
  fix freed pointer access when it is in use by other threads, and get
  rid of potential memory/fd leak.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43112 b2dd03c8-39d4-4d8f-98ff-823fe69b080e