Improve performance of issue and MR finders used without group/project scope

Summary

Search returns 500. Whoops, something went wrong on our end.

Steps to reproduce

Open this URL https://gitlab.com/search?utf8=%E2%9C%93&search=Project+ID%3A+&group_id=&project_id=13083&search_code=true&repository_ref=master

Example Project

https://gitlab.com/gitlab-org/gitlab-ce

What is the current bug behavior?

Search returns 500

What is the expected correct behavior?

Search should display results

Output of checks

This bug happens on GitLab.com