[Elastic] Stabilize database indexer if database is inconsistent

CHANGELOG-EE

@@ -3,6 +3,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 v 8.7.0 (unreleased)
   - Update GitLab Pages to 0.2.1: support user-defined 404 pages
   - Refactor group sync to pull access level logic to its own class. !306
+  - [Elastic] Stabilize database indexer if database is inconsistent
 
 v 8.6.5
   - No EE-specific changes

lib/elastic/issues_search.rb

@@ -38,8 +38,8 @@ module Elastic
           data[attr.to_s] = self.send(attr)
         end
 
-        data['project'] = { 'id' => project.id }
-        data['author'] = { 'id' => author.id }
+        data['project'] = { 'id' => project_id }
+        data['author'] = { 'id' => author_id }
         data['updated_at_sort'] = updated_at
         data
       end

lib/elastic/merge_requests_search.rb

@@ -58,7 +58,7 @@ module Elastic
 
         data['source_project'] = { 'id' => source_project_id }
         data['target_project'] = { 'id' => target_project_id }
-        data['author'] = { 'id' => author.id }
+        data['author'] = { 'id' => author_id }
         data['updated_at_sort'] = updated_at
         data
       end