Adult PIN Issue

*I'm submitting a ...*
- [x] bug report
- [ ] feature request
- [ ] support request

## General infomration
No content can be viewed by additional users due to PIN issue.

### Prerequisites

* [x] Are you running the latest version?

### Description

I have 3 users on my Netflix account.
User1: No age restrictions (account owner)
User2: Guidance restriction
User3: Older kids restriction

When requesting any episode in any account the ‘adult pin’ is requested. For user 1 this isn’t a problem as most/all content is 15 or 18+. User 2 and 3 both return ‘adult verification failed: please check your adult pin’ message. If pin field is left blank (because no pin is required) it returns the same message.

### Steps to Reproduce

1. Use any Netflix account user
2. Select non-age restricted programme (i.e. program with requirement for PIN insertion)
3. Input pin/leave PIN field blank, press OK
4. Recieve error message

**Expected behavior:** [What you expected to happen]
PIN Request to not happen and programme to be played (for non restricted content)

**Actual behavior:** [What actually happened]
PIN Request for 'non restricted' content. Regardless if PIN entered or left blank. Programme does not play

## Context (Environment)
Raspberry Pi3. Running Kodi 18 (not nightly build) in OSMC

### Installation

* [x] I installed the plugin via zip from the Releases page
* [ ] I´m using the Netflix Repo
* [ ] I´m using a different source (Please tell which)

### Operating System

* [ ] Linux (x86/x64)
* [ ] OSX (x86/x64)
* [ ] Windows (x86/x64)
* [x] Linux (ARM)
* [ ] Android

Start by reproducing the adult PIN flow on Kodi 18 running on OSMC with three Netflix profiles, using the listed steps. Trace how unrestricted and restricted programmes are classified and how blank or valid PIN input is handled; done means unrestricted content plays without an unnecessary prompt while restricted content still verifies correctly.

Written by the indexing model from the issue text.