Fix crash when handling a dialog result

[emawby]

Description

One Line Summary

Fix a crash when handling a dialog result (often from requesting location or notification permission when permission has already been denied.)

Details

The stack traces point to crashing when calling [self.queue removeObjectAtIndex:0]; in delayResult. This was never reproducible as the queue should never be empty when calling delayResult, but this PR adds thread safety and a sanity check to protect and this crash.

• Synchronize queue reads and writes on self.queue

• Additionally verify that queue.count > 0 prior to removing object at index 0

Motivation

Fix crash

Scope

iOS dialogs

Testing

Unit testing

no infrastructure in place yet for mocking handling prompting actions

Manual testing

Tested by spamming the permission dialog actions

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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This change is 

[nan-li]

Do you know if there are consequences to calling displayDialog within the lock?

[emawby]

Do you know if there are consequences to calling displayDialog within the lock?

I moved the calls outside of the sync blocks since I don't think they need to be inside. Both had the same results when testing, but this seems better.