授权访问子群组，子群组没有项目就报404

Summary

在群组geo-admin-test下面新建子群组geo-admin-test/gitlab-jh-test，对用户xmtang授权子群组gitlab-jh-test的访问权限，如果子群组下面还没有项目，那么被授权用户xmtang登录之后选择我的群组，显示为父群组geo-admin-test的名称，点击访问群组gitlab-jh-test提示404。

如果在浏览器的URL 后面手动补齐路径就可以访问到，例如:http://43.134.231.15/geo-admin-test 结果为404；http://43.134.231.15/geo-admin-test/gitlab-jh-test 访问正常。

如果在子群组gitlab-jh-test 下面创建有项目，则访问正常，删除所有项目后，访问又变成404。

Steps to reproduce

Example Project

What is the current bug behavior?

What is the expected correct behavior?

Relevant logs and/or screenshots

给用户授权子群组

用户xmtang没有父群组权限

用xmtang用户登录查看群组，显示为父群组名称

点击访问群组提示404

手动补齐URL 可以访问

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes