Fix bug where non-project members of the target project could set labels on new merge requests.

(cherry picked from commit 77e508d8)

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 7.14.0 (unreleased)
+  - Fix bug where non-project members of the target project could set labels on new merge requests.
   - Update default robots.txt rules to disallow crawling of irrelevant pages (Ben Bodenmiller)
   - Fix redirection after sign in when using auto_sign_in_with_provider
   - Upgrade gitlab_git to 7.2.14 to ignore CRLFs in .gitmodules (Stan Hu)

app/views/shared/issuable/_form.html.haml

@@ -38,7 +38,7 @@
       .clearfix
       .error-alert
   %hr
-- if can?(current_user, :"admin_#{issuable.to_ability_name}", @project)
+- if can?(current_user, :"admin_#{issuable.to_ability_name}", issuable.project)
   .form-group
     .issue-assignee
       = f.label :assignee_id, class: 'control-label' do