Refine offense range for Lint/SafeNavigationWithEmpty

[koic]

This PR refines offense range for Lint/SafeNavigationWithEmpty.

The following is an example.

return unless foo&.empty?

Before

% bundle exec rubocop example.rb --only Lint/SafeNavigationWithEmpty
(snip)

Offenses:

example.rb:1:1: W: Lint/SafeNavigationWithEmpty: Avoid calling empty?
with the safe navigation operator in conditionals.
return unless foo&.empty?
^^^^^^^^^^^^^^^^^^^^^^^^^

1 file inspected, 1 offense detected

After

% bundle exec rubocop example.rb --only Lint/SafeNavigationWithEmpty
(snip)

Offenses:

example.rb:1:15: W: Lint/SafeNavigationWithEmpty: Avoid calling empty?
with the safe navigation operator in conditionals.
return unless foo&.empty?
              ^^^^^^^^^^^

1 file inspected, 1 offense detected

---

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.