Fix duplicate given order creating answers

It's possible to have a given order greater than the number of answers;
we don't have any validation rules for that. So the check for the number
of answers isn't enough.

Checking the maximum given order in the answers is safer. Another option
would be to reorder the answers every time we add a new one, but I'm not
sure whether that's the expected behaviour.

Note even after this change the action is not thread-safe, as it is
possible to create two questions with the same given order with two
simultaneous requests.

app/controllers/polls/answers_controller.rb

@@ -9,7 +9,7 @@ class Polls::AnswersController < ApplicationController
     if @question.votation_type.open? && !check_question_answer_exist
       @question.question_answers.create(
         title: params[:answer],
-        given_order: @question.question_answers.count + 1,
+        given_order: @question.question_answers.maximum(:given_order).to_i + 1,
         hidden: false
       )
       flash.now[:notice] = t("dashboard.polls.index.succesfull")

spec/features/polls/votation_type_spec.rb

@@ -320,6 +320,17 @@ describe "Poll Votation Type" do
         expect(page).to have_link "Added answer", class: "answered"
       end
     end
+
+    scenario "existing given order is bigger than the number of answers", :js do
+      answer1.update(given_order: question.question_answers.count + 1)
+
+      visit poll_path(poll_current)
+
+      fill_in "answer", with: "Added answer"
+      click_button "Add answer"
+
+      expect(page).to have_link "Added answer"
+    end
   end
 
   context "Answers set" do