Retrieve current ADM PurchasingListener assuming it returns a nullable.

[brismithers]

Description

One Line Summary

Update TrackAmazonPurchase.onUnfocused to retrieve the PurchasingListener assuming it can be null.

Details

This builds on top of #1860, the same logic applies. However if a user unfocuses the application early enough during initialization, the TrackAmazonPurchase.onUnfocused will be called. This also retrieves the current PurchasingListener, which can be null.

The statement was also switched from index notation to use .get, similar to the initialization logic, to keep things consistent.

Motivation

#1812

Testing

Unit testing

No unit tests were added

Manual testing

Tested on Android emulator API 33

1. Add dependency 'com.amazon.device:amazon-appstore-sdk:3.0.3' to Demo App
2. Reproduced the crash by unfocusing the app when the splash screen shows
3. Then test everything is working after this fix

Affected code checklist

• Notifications
  • Display
  • Open
  • Push Processing
  • Confirm Deliveries
• Outcomes
• Sessions
• In-App Messaging
• REST API requests
• Public API changes

Checklist

Overview

• I have filled out all REQUIRED sections above
• PR does one thing
  • If it is hard to explain how any codes changes are related to each other then it most likely needs to be more than one PR
• [] Any Public API changes are explained in the PR details and conform to existing APIs

Testing

• I have included test coverage for these changes, or explained why they are not needed
• All automated tests pass, or I explained why that is not possible
• I have personally tested this on my device, or explained why that is not possible

Final pass

• Code is as readable as possible.
  • Simplify with less code, followed by splitting up code into well named functions and variables, followed by adding comments to the code.
• I have reviewed this PR myself, ensuring it meets each checklist item
  • WIP (Work In Progress) is ok, but explain what is still in progress and what you would like feedback on. Start the PR title with "WIP" to indicate this.

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