CRM-20393 - fix for check if the user already submitted transaction

[KarinG]

No need to truncate x_invoice_num - and without truncating x_invoice_num which is passed into this function as invoiceId - this can actually work now:

  /**
   * Checks to see if invoice_id already exists in db.
   *
   * It's arguable if this belongs in the payment subsystem at all but since several processors implement it
   * it is better to standardise to being here.
   *
   * @param int $invoiceId The ID to check.
   *
   * @param null $contributionID
   *   If a contribution exists pass in the contribution ID.
   *
   * @return bool
   *   True if invoice ID otherwise exists, else false
   */
  protected function checkDupe($invoiceId, $contributionID = NULL) {
    $contribution = new CRM_Contribute_DAO_Contribution();
    $contribution->invoice_id = $invoiceId;
    if ($contributionID) {
      $contribution->whereAdd("id <> $contributionID");
    }
    return $contribution->find();
  }

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• CRM-20393: Authorize.net: fix for the "check if the user already submitted this transaction"

[eileenmcnaughton]

I think this is a fairly clear-cut of A.net either accepts or doesn't accept > 20 char & if @KarinG has tested it I think we can merge on pass