Fix a bug displaying project commit anchors

A repository can be non-empty, yet lack a root_ref. When this is the
case, we fail to generate a link to commits, resulting in a 500 error.

Using the "default" default branch in this case allows us to generate a
link. It leads to a location that will 404, but that's a better outcome
than the current scenario.

Changelog: fixed

app/presenters/project_presenter.rb

@@ -210,7 +210,7 @@ class ProjectPresenter < Gitlab::View::Presenter::Delegated
                      strong_start: '<strong class="project-stat-value">'.html_safe,
                      strong_end: '</strong>'.html_safe
                    },
-                   empty_repo? ? nil : project_commits_path(project, repository.root_ref))
+                   empty_repo? ? nil : project_commits_path(project, default_branch_or_main))
   end
 
   def branches_anchor_data

changelogs/unreleased/329862-fix-project-path-generation.yml

+---
+title: Fix a bug displaying project commit anchors
+merge_request: 61361
+author:
+type: fixed