Fix a false positive for Style/SafeNavigation

[koic]

This PR fixes the following error for Style/SafeNavigation when checking foo&.empty? in a conditional.

% cat example.rb
do_something if ENV['VERSION'] && ENV['VERSION'].empty?

% bunble exec rubocop -a example.rb --only Style/SafeNavigation,Lint/SafeNavigationWithEmpty
(snip)

Inspecting 1 file
W

Offenses:

example.rb:1:17: W: [Corrected] Lint/SafeNavigationWithEmpty: Avoid
calling empty? with the safe navigation operator in conditionals.
do_something if ENV['VERSION']&.empty?
                ^^^^^^^^^^^^^^^^^^^^^^
example.rb:1:17: C: [Corrected] Style/SafeNavigation: Use safe
navigation (&.) instead of checking if an object exists before calling
the method.
do_something if ENV['VERSION'] && ENV['VERSION'].empty?
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

0 files inspected, 2 offenses detected, 2 offenses corrected
Infinite loop detected in
/Users/koic/src/github.com/koic/rubocop-issues/rails/example.rb.
/Users/koic/src/github.com/rubocop-hq/rubocop/lib/rubocop/runner.rb:289:in
`check_for_infinite_loop'
/Users/koic/src/github.com/rubocop-hq/rubocop/lib/rubocop/runner.rb:272:in
`block in iterate_until_no_changes'
/Users/koic/src/github.com/rubocop-hq/rubocop/lib/rubocop/runner.rb:271:in
`loop'
/Users/koic/src/github.com/rubocop-hq/rubocop/lib/rubocop/runner.rb:271:in
`iterate_until_no_changes'
/Users/koic/src/github.com/rubocop-hq/rubocop/lib/rubocop/runner.rb:242:in
`do_inspection_loop'

I found it with the following code.
https://github.com/rails/rails/blob/v6.0.3.2/activerecord/lib/active_record/railties/databases.rake#L120

---

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[bbatsov]

Looks good!