Fix an error for Lint/UselessTimes

[koic]

This PR fixes the following error for Lint/UselessTimes when using empty block argument.

% cat example.rb
def foo
  1.times do
  end
end

% rubocop --only Lint/UselessTimes -d
(snip)

Inspecting 1 file
Scanning /Users/koic/src/github.com/koic/rubocop-issues/bar/example.rb
An error occurred while Lint/UselessTimes cop was inspecting
/Users/koic/src/github.com/koic/rubocop-issues/bar/example.rb:2:2.
undefined method `source' for nil:NilClass
/Users/koic/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/rubocop-0.91.0/lib/rubocop/cop/lint/useless_times.rb:76:in `autocorrect_block'
/Users/koic/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/rubocop-0.91.0/lib/rubocop/cop/lint/useless_times.rb:57:in `block in on_send'
/Users/koic/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/rubocop-0.91.0/lib/rubocop/cop/base.rb:333:in `correct'
/Users/koic/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/rubocop-0.91.0/lib/rubocop/cop/base.rb:126:in `add_offense'
/Users/koic/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/rubocop-0.91.0/lib/rubocop/cop/lint/useless_times.rb:49:in `on_send'

---

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.

[dvandersluis]

Maybe instead of updating autocorrect_block, the condition can be updated here to include when the node has an empty body: https://github.com/rubocop-hq/rubocop/blob/354da8b53a41183948f6a6c09053ffee937b7d5e/lib/rubocop/cop/lint/useless_times.rb#L52-L53

Then the remove node logic won't have to be duplicated.

[koic]

Sure! I updated this PR. Thank you for your suggestion!

[bbatsov]

Thanks!