Fix a build error

This PR prevents the following build error:

```console
NoMethodError:
  undefined method `cop_name' for nil
# ./lib/rubocop/cop/badge.rb:52:in `match?'
# ./lib/rubocop/cop/registry.rb:300:in `resolve_badge'
# ./vendor/bundle/ruby/3.3.0/gems/rubocop-rspec_rails-2.28.3/lib/rubocop-rspec_rails.rb:30:in `qualified_cop_name'
```

https://github.com/rubocop/rubocop/actions/runs/8656558784/job/23737409762

This build error is due to a monkey patch in rubocop-rails_rails:
rubocop/rubocop-rspec_rails#14

The monkey patch in rubocop-rspec_rails should also be fixed, but this patch prevents RuboCop from failing due to dependencies.
RuboCop does not depend on Rails, so the ideal solution would be to remove the dependency on rubocop-rspec_rails gem.
However, this is not possible currently because rubocop-rspec is still dependent on it.

lib/rubocop/cop/registry.rb

@@ -297,6 +297,10 @@ def with(cops)
       end
 
       def resolve_badge(given_badge, real_badge, source_path)
+        # Prevents the following build error:
+        # https://github.com/rubocop/rubocop/actions/runs/8656558784/job/23737409762
+        return '' if read_badge.nil?
+
         unless given_badge.match?(real_badge)
           path = PathUtil.smart_path(source_path)
           warn "#{path}: #{given_badge} has the wrong namespace - " \