API: Fix recursive flag not working with Rugged get_tree_entries flag

Attempting to use the API endpoint
/projects/:id/repository/tree?recursive=true would only return a subset
of the results since the full recursive list wasn't actually being
returned.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/61979

changelogs/unreleased/sh-fix-rugged-get-tree-entries-recursive.yml

+---
+title: Fix Rugged get_tree_entries recursive flag not working
+merge_request: 28494
+author:
+type: fixed

lib/gitlab/git/rugged_impl/tree.rb

@@ -43,6 +43,8 @@ module Gitlab
                 ordered_entries.concat(tree_entries_from_rugged(repository, sha, entry.path, true))
               end
             end
+
+            ordered_entries
           end
 
           def rugged_populate_flat_path(repository, sha, path, entries)

spec/lib/gitlab/git/tree_spec.rb

@@ -19,7 +19,9 @@ describe Gitlab::Git::Tree, :seed_helper do
     it 'returns a list of tree objects' do
       entries = described_class.where(repository, SeedRepo::Commit::ID, 'files', true)
 
-      expect(entries.count).to be >= 5
+      expect(entries.map(&:path)).to include('files/html',
+                                             'files/markdown/ruby-style-guide.md')
+      expect(entries.count).to be >= 10
       expect(entries).to all(be_a(Gitlab::Git::Tree))
     end