* eval.c (rb_f_autoload): check if ruby_cbase is nil (during
  instance_eval for objects cannot have singleton classes,
  e.g. fixnums and symbols).  [ruby-dev:28178]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@9912 b2dd03c8-39d4-4d8f-98ff-823fe69b080e