Merge branch 'fix-protected-branches-routing' into 'master'

Fix protected branches routing

### Summary

On the master branch, if you attempt to access the protected branches in the project settings with an empty repo, you get `NoMethodError - undefined method "project_url"`.

### Steps to reproduce

1. Check out GitLab master and run.
2. Create a new project.
3. Go to Settings.
4. Click on "Protected branches"

### Expected behavior

The controller is supposed to redirect back to the projects page since there are no branches.

### Observed behavior

Internal Error 500

### Relevant logs

```
NoMethodError - undefined method `project_url' for #<Projects::ProtectedBranchesController:0x007fd920054af0>:
  app/controllers/application_controller.rb:157:in `method_missing'
  actionpack (4.1.9) lib/action_dispatch/routing/polymorphic_routes.rb:142:in `polymorphic_url'
  actionpack (4.1.9) lib/action_dispatch/routing/url_for.rb:161:in `url_for'
  actionpack (4.1.9) lib/action_controller/metal/redirecting.rb:91:in `_compute_redirect_to_location'
  turbolinks (2.0.0) lib/turbolinks.rb:15:in `_compute_redirect_to_location_with_xhr_referer'
  actionpack (4.1.9) lib/action_controller/metal/redirecting.rb:71:in `redirect_to
```

### Fix

I added a unit test for the empty project case and replicated the issue. I added the URL router helpers that appear to be necessary after 42387b733b.

See merge request !359

app/helpers/gitlab_routing_helper.rb

@@ -28,4 +28,20 @@ module GitlabRoutingHelper
   def merge_request_path(entity, *args)
     namespace_project_merge_request_path(entity.project.namespace, entity.project, entity, *args)
   end
+
+  def project_url(project, *args)
+    namespace_project_url(project.namespace, project, *args)
+  end
+
+  def edit_project_url(project, *args)
+    edit_namespace_project_url(project.namespace, project, *args)
+  end
+
+  def issue_url(entity, *args)
+    namespace_project_issue_url(entity.project.namespace, entity.project, entity, *args)
+  end
+
+  def merge_request_url(entity, *args)
+    namespace_project_merge_request_url(entity.project.namespace, entity.project, entity, *args)
+  end
 end

spec/controllers/projects/protected_branches_controller_spec.rb

@@ -0,0 +1,10 @@
+require('spec_helper')
+
+describe Projects::ProtectedBranchesController do
+  describe "GET #index" do
+    let(:project) { create(:project_empty_repo, :public) }
+    it "redirect empty repo to projects page" do
+      get(:index, namespace_id: project.namespace.to_param, project_id: project.to_param)
+    end
+  end
+end