Fix IAM Tag Sub crash when getTags returns after loading HTML

[emawby]

Description

One Line Summary

This PR fixes a crash when displaying IAMs with tag sub in a specific timing scenario.

Details

When loading tags for IAM tag sub we load the tags and the HTML content for the IAM in parallel. There was no issue when the getTags request finished prior to loading the HTML, but if loading HTML finished first the App would crash. This is because the getTags request returns on a background thread and calls setWaitForTags on that bg thread. setWaitForTags then instructs the webView to display with the HTML content, but doing so on a background thread is not allowed since it is a UI element. We need to dispatch to the main thread to avoid crashes.

Motivation

Fixes IAM crash

Testing

Manual testing

I have tested IAMs with tag sub on my iPhone when both timing scenarios occur as well as IAMs without tag sub.

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
• 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
  We don't have a good way to test UI bg thread issues without UI tests
• 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)

[jkasten2]

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @nan-li)