Fix crashes when failing to download Notification attachments

[emawby]

Fixes #586 and Unity crash 411

Description

One Line Summary

This PR prevents crashes due to failures when writing downloaded notification attachments (images) to a temporary file location.

Details

These crashes are not easily reproduce-able, but can happen in the following scenarios according to Apple

This method raises NSFileHandleOperationException if the file descriptor is closed or isn’t valid, if the handle represents an unconnected pipe or socket endpoint, if there isn’t any free space on the file system, or if any other writing error occurs.

For iOS 13+ devices we will now use writeData:error: which returns a boolean and populates the NSError parameter with the failure reason if it fails.

For < iOS 13 we will place a try catch around writeData: to avoid crashes.

In both cases we will log the failure reason. Note that this is logged on the NotificationServiceExtension process not the main app process.

Motivation

Prevent the crashes below
#586 and Unity crash 411

Testing

Manual testing

I tested on an iOS 15 device that uses the new writeData:error: API. However I was unable to reproduce a failure.

Affected code checklist

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

Checklist

Overview

• I have filled out all REQUIRED sections above
• PR does one thing
• 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.
• I have reviewed this PR myself, ensuring it meets each checklist item

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This change is 

[jkasten2]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @nan-li)