Merge branch 'mirror-empty-repo' into 'master'

Don't redirect away from Mirror Repository settings when repo is empty

Fixes #217

See merge request !135

CHANGELOG-EE

@@ -2,6 +2,7 @@ v 8.5.0 (unreleased)
 v 8.4.2
   - Elasticsearch indexer performance improvements
+  - Don't redirect away from Mirror Repository settings when repo is empty.
 v 8.4.1
   - No EE-specific changes

app/controllers/projects/mirrors_controller.rb

 class Projects::MirrorsController < Projects::ApplicationController
   # Authorize
-  before_action :require_non_empty_project
   before_action :authorize_admin_project!, except: [:update_now]
   before_action :authorize_push_code!, only: [:update_now]