Fix commits list 500 with multi-file editor new_repo cookie

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/39821

/<namespace>/<project>/commmits/master

app/views/shared/_ref_switcher.html.haml

+- show_create = local_assigns.fetch(:show_create, false)
+
 - show_new_branch_form = show_new_repo? && show_create && can?(current_user, :push_code, @project)
 - dropdown_toggle_text = @ref || @project.default_branch
 = form_tag switch_project_refs_path(@project), method: :get, class: "project-refs-form" do

changelogs/unreleased/39821-fix-commits-list-with-multi-file-editor.yml

+---
+title: Fix commits page throwing 500 when the multi-file editor was enabled
+merge_request: 15502
+author:
+type: fixed

spec/features/commits_spec.rb

@@ -202,5 +202,12 @@ describe 'Commits' do
         expect(page).to have_content("committed #{commit.committed_date.strftime("%b %d, %Y")}")
       end
     end
+
+    it 'shows the ref switcher with the multi-file editor enabled', :js do
+      set_cookie('new_repo', 'true')
+      visit project_commits_path(project, branch_name)
+
+      expect(find('.js-project-refs-dropdown')).to have_content branch_name
+    end
   end
 end