Don't allow to modify answer's images for started polls

Note that the `create` action doesn't create an image but updates an
answer instead. We're removing the references to `:create` in the
abilities since it isn't used.

In the future we might change the form to add an image to an answer
because it's been broken for ages since it shows all the attached
images.

spec/controllers/admin/poll/questions/answers/images_controller_spec.rb

@@ -0,0 +1,52 @@
+require "rails_helper"
+
+describe Admin::Poll::Questions::Answers::ImagesController, :admin do
+  let(:current_answer) { create(:poll_question_answer, poll: create(:poll)) }
+  let(:future_answer) { create(:poll_question_answer, poll: create(:poll, :future)) }
+
+  describe "POST create" do
+    let(:answer_attributes) do
+      {
+        images_attributes: {
+          "0" => {
+            attachment: fixture_file_upload("clippy.jpg"),
+            title: "Title",
+            user_id: User.last.id
+          }
+        }
+      }
+    end
+
+    it "is not possible for an already started poll" do
+      post :create, params: { poll_question_answer: answer_attributes, answer_id: current_answer }
+
+      expect(flash[:alert]).to eq "You do not have permission to carry out the action 'update' on Answer."
+      expect(Image.count).to eq 0
+    end
+
+    it "is possible for a not started poll" do
+      post :create, params: { poll_question_answer: answer_attributes, answer_id: future_answer }
+
+      expect(response).to redirect_to admin_answer_images_path(future_answer)
+      expect(flash[:notice]).to eq "Image uploaded successfully"
+      expect(Image.count).to eq 1
+    end
+  end
+
+  describe "DELETE destroy" do
+    it "is not possible for an already started poll" do
+      current_image = create(:image, imageable: current_answer)
+      delete :destroy, xhr: true, params: { id: current_image }
+
+      expect(flash[:alert]).to eq "You do not have permission to carry out the action 'destroy' on Image."
+      expect(Image.count).to eq 1
+    end
+
+    it "is possible for a not started poll" do
+      future_image = create(:image, imageable: future_answer)
+      delete :destroy, xhr: true, params: { id: future_image }
+
+      expect(Image.count).to eq 0
+    end
+  end
+end