Check if commit exists first in commit status API

lib/api/commit_statuses.rb

@@ -20,8 +20,8 @@ module API
       get ':id/repository/commits/:sha/statuses' do
         authorize!(:read_commit_status, user_project)
-        ci_commit = user_project.ci_commit(params[:sha])
         not_found!('Commit') unless user_project.commit(params[:sha])
+        ci_commit = user_project.ci_commit(params[:sha])
         return [] unless ci_commit
         statuses = ci_commit.statuses