* gc.c (obj_memsize_of): memsize_of(T_ZOMBIE) returns 0, not a rb_bug.
  ObjectSpace.count_objects_size() uses memsize_of(T_ZOMBIE).
  This bug introduced at r46348.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46455 b2dd03c8-39d4-4d8f-98ff-823fe69b080e