Fixes missing reference for claim

If the form is invalid, say the journey session has already been
submitted and the user double clicks the submit button, we need to
return early from the child `save` method to avoid calling the mailer
with a claim that hasn't been saved (which triggeres an error as the
claim has no reference number).

app/forms/claim_submission_base_form.rb

@@ -27,6 +27,8 @@ def save
 
     ClaimMailer.submitted(claim).deliver_later
     ClaimVerifierJob.perform_later(claim)
+
+    true
   end
 
   private

app/forms/journeys/further_education_payments/claim_submission_form.rb

@@ -2,7 +2,7 @@ module Journeys
   module FurtherEducationPayments
     class ClaimSubmissionForm < ::ClaimSubmissionBaseForm
       def save
-        super
+        return false unless super
 
         if Policies::FurtherEducationPayments.duplicate_claim?(claim)
           claim.eligibility.update!(flagged_as_duplicate: true)

spec/forms/journeys/further_education_payments/claim_submission_form_spec.rb

@@ -108,9 +108,12 @@
       ).and_return(double(deliver_later: nil))
 
       first_claim_form = described_class.new(journey_session: journey_session)
-      second_claim_form = described_class.new(journey_session: journey_session)
 
       first_claim_form.save
+
+      journey_session.update! claim: nil
+      second_claim_form = described_class.new(journey_session: journey_session)
+
       second_claim_form.save
 
       expect(ClaimMailer).to(