Fix poll API not requiring authentication on non-public polls (#10960)

* Fix poll API not requiring authentication on non-public polls

That API does not reveal the content of the status, i.e. the question
itself, nor who the author is, nor which status it belongs to, but it
does reveal the poll options and how many answers they got

Fix #10959

* Add test

spec/controllers/api/v1/polls_controller_spec.rb

@@ -10,14 +10,26 @@ RSpec.describe Api::V1::PollsController, type: :controller do
   before { allow(controller).to receive(:doorkeeper_token) { token } }
 
   describe 'GET #show' do
-    let(:poll) { Fabricate(:poll) }
+    let(:poll) { Fabricate(:poll, status: Fabricate(:status, visibility: visibility)) }
 
     before do
       get :show, params: { id: poll.id }
     end
 
-    it 'returns http success' do
-      expect(response).to have_http_status(200)
+    context 'when parent status is public' do
+      let(:visibility) { 'public' }
+
+      it 'returns http success' do
+        expect(response).to have_http_status(200)
+      end
+    end
+
+    context 'when parent status is private' do
+      let(:visibility) { 'private' }
+
+      it 'returns http not found' do
+        expect(response).to have_http_status(404)
+      end
     end
   end
 end