Fix application client count

Display the number of unique users with an access token instead of the
total number of access tokens per application in the admin area.

CHANGELOG

@@ -53,7 +53,7 @@ v 7.8.0 (unreleased)
   - Show assignees in merge request index page (Kelvin Mutuma)
   - Link head panel titles to relevant root page.
   - Allow users that signed up via OAuth to set their password in order to use Git over HTTP(S).
-  - Fix duplicate authorized applications in user profile.
+  - Fix duplicate authorized applications in user profile and incorrect application client count in admin area.
 
 v 7.7.2
   - Update GitLab Shell to version 2.4.2 that fixes a bug when developers can push to protected branch

app/views/admin/applications/index.html.haml

@@ -17,6 +17,6 @@
       %tr{:id => "application_#{application.id}"}
         %td= link_to application.name, admin_application_path(application)
         %td= application.redirect_uri
-        %td= application.access_tokens.count
+        %td= application.access_tokens.map { |t| t.resource_owner_id }.uniq.count
         %td= link_to 'Edit', edit_admin_application_path(application), class: 'btn btn-link'
         %td= render 'delete_form', application: application