* gc.c (obj_memsize_of): don't calculate memsize of T_NODE
  when called from check_gen_consistency. It fixes segmentation
  fault on RGENGC_CHECK_MODE >= 1 introduced by r47188.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47208 b2dd03c8-39d4-4d8f-98ff-823fe69b080e