Security Dashboard fails to load when location isn't present

Summary

The security dashboard is failing when vulnerabilities do not have a location attribute.

Steps to reproduce

Run Container Scanning or DAST on a project and if they have vulnerabilities, the dashboard will fail to load.

Relevant logs and/or screenshots

TypeError at /groups/reports/-/security/vulnerabilities
=======================================================
> no implicit conversion of nil into String
ee/app/presenters/vulnerabilities/occurrence_presenter.rb, line 25
------------------------------------------------------------------

   20           complete_path << "-#{end_line}" if end_line
   21         end
   22       end
   23   
   24       def vulnerability_path
>  25         @vulnerability_path ||= project_blob_path(project, File.join(sha, location['file']))
   26       end
   27     end
   28   end

App backtrace
-------------
 - ee/app/presenters/vulnerabilities/occurrence_presenter.rb:25:in `vulnerability_path'
 - ee/app/presenters/vulnerabilities/occurrence_presenter.rb:16:in `add_line_numbers'
 - ee/app/presenters/vulnerabilities/occurrence_presenter.rb:10:in `blob_path'
 - ee/app/serializers/vulnerabilities/occurrence_entity.rb:27:in `block in <class:OccurrenceEntity>'
 - app/serializers/base_serializer.rb:16:in `represent'
 - app/serializers/concerns/with_pagination.rb:19:in `represent'
 - ee/app/serializers/vulnerabilities/occurrence_serializer.rb:17:in `represent'
 - ee/app/controllers/groups/security/vulnerabilities_controller.rb:14:in `block (2 levels) in index'
 - ee/app/controllers/groups/security/vulnerabilities_controller.rb:9:in `index'
 - lib/gitlab/i18n.rb:55:in `with_locale'
 - lib/gitlab/i18n.rb:61:in `with_user_locale'