Create group called 'project' then rename cause alll project avatar lost

Summary

Create group called 'project' then rename cause alll project avatar lost

Steps to reproduce

1. Set avatar for exist project
2. Create group called 'project'
3. Rename 'project' group to other name
4. Check project list, all project avatar lost.

/var/opt/gitlab/gitlab-rails/uploads/project is conflict with project name.

What is the current bug behavior?

'project' folder conflict with group named 'project', rename it cause project folder lost

What is the expected correct behavior?

Should not allow create project named "project"

Results of GitLab environment info

GitLab 8.17.0 on Ubuntu 16.04 LTS