InfinityLoader.willDestroy incorrectly assumes `inifinityModel` is still valid

[trevordevore]

After updating to ember-infinity 3.0.0 I'm seeing the following error when transitioning to a new route:

global failure: TypeError: Cannot read properties of undefined (reading 'off')
Source:
TypeError: Cannot read properties of undefined (reading 'off')

The error occurs in addon/components/infinity-loader.js#willDestroy because infinityModel is null. I see that in commit
9b6956b the check for isDestroyed was added because of the same error after a route change.

The difference in my situation is that isDestroyed is false BUT isDestroying is true. In my case the infinityModel has already been nullified at this point.

Context

The application is running Ember 3.28 and is being prepared for an upgraded to 4. I tested the same code with Ember 4.0.1 but got the same result.

[trevordevore]

I've created a PR with a suggested change that fixes the bug in my application. Since _loadStatusDidChange has an early exit if isDestroying or isDestroyed this seemed like a safe approach.