handle exception in Rails/RedundantReceiverInWithOptions with empty body

[ericsullivan]

I ran rubocop on our test suite and encountered an exception in Rails/RedundantReceiverInWithOptions caused by the block:

with_options if: :state? do |_object|
end

I'm not sure if it should ignore the block (the approach I took here) or flag it as unnecessary. In either case, I don't think it should raise an exception so I wanted to add this PR now, and if it should produce an error I can open an issue.

---

Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[ericsullivan]

I'm not sure what happened with the ci/circleci: ruby-2.3-spec job. Is that related to this PR or a known issue?

[koic]

Occasionally CircleCI makes a mistake in the report. It seems that this has occurred.
This changes look good to me. Can you squash your commits into one?

[ericsullivan]

squashed, thanks for reviewing @koic

[koic]

Thanks too!