Don't allow to modify questions for started polls

Adding, modifiying, and/or deleting questions for an already started
poll is far away from being democratic and can lead to unwanted side
effects like missing votes in the results or stats.

So, from now on, only modifiying questions will be possible only if
the poll has not started yet.

spec/components/admin/poll/questions/form_component_spec.rb

@@ -0,0 +1,37 @@
+require "rails_helper"
+
+describe Admin::Poll::Questions::FormComponent do
+  before { sign_in(create(:administrator).user) }
+
+  context "question with a poll" do
+    let(:poll) { create(:poll) }
+    let(:question) { Poll::Question.new(poll: poll) }
+
+    it "does not display the poll selector" do
+      render_inline Admin::Poll::Questions::FormComponent.new(question, url: "/")
+
+      expect(page).not_to have_select "Poll"
+      expect(page).to have_field "poll_question[poll_id]", type: :hidden, with: poll.id
+    end
+  end
+
+  context "question without a poll" do
+    let(:question) { Poll::Question.new }
+
+    it "allows selecting polls which have not already started" do
+      create(:poll, :future, name: "Future poll")
+
+      render_inline Admin::Poll::Questions::FormComponent.new(question, url: "/")
+
+      expect(page).to have_select "Poll", options: ["Select Poll", "Future poll"]
+    end
+
+    it "does not allow selecting polls which have already started" do
+      create(:poll, name: "Already started poll")
+
+      render_inline Admin::Poll::Questions::FormComponent.new(question, url: "/")
+
+      expect(page).to have_select "Poll", options: ["Select Poll"]
+    end
+  end
+end