Fix --ignore-unrecognized-cops option always showing empty warning even if there was no problem

[nobuyo]

The internal condition was wrong, and the message The following cops or departments are ... was always displayed with just the option is specified.

Reported at: #10630 (comment)

$ bundle exec rubocop --ignore-unrecognized-cops
The following cops or departments are not recognized and will be ignored: # <--- 👀 

Inspecting 2 files
.W

...

---

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• 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.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.

[pirj]

Thanks!