[Bug]: Crash in finaliser if RealmObject implementation throws in object initialisation

[peppy]

What happened?

Regressed in 2d2f595#diff-ffe0558165702693f2ba96b95df2b7f6bf559ca7a2ef344e9cab6af24f75f6ae (due to missing null check).

This is a bit of a caveat with NRT and pre-constructor time crashes. We get around similar issues by using a helper method to check for null (https://github.com/ppy/osu-framework/blob/7fea93e6f5a30d5a47e2bd609fe1cf7ef45c507d/osu.Framework/Extensions/ObjectExtensions/ObjectExtensions.cs#L30-L33, usage: https://github.com/ppy/osu-framework/blob/3a9acd01eac691fcbea0163038743a05bb0ba41d/osu.Framework/IO/Stores/RawCachingGlyphStore.cs#L178). Another way would be to make the _accessor nullable

With the sample code included below, a crash is observed which can halt an application that is not manually handling all unobserved exceptions:

JetBrains.Rider-EAP.2022-10-05.at.07.58.44.mp4

Repro steps

• Have a class that throws an exception before reaching the constructor (ie. object initialisers).
• Observe crash on first GC/finalize operation.

Version

10.16.0

What SDK flavour are you using?

Local Database only

What type of application is this?

Console/Server

Client OS and version

n/a

Code snippets

// See https://aka.ms/new-console-template for more information

using System.Diagnostics;
using Realms;

while (true)
{
    try
    {
        var model = new TestModel();
    }
    catch (Exception e)
    {
        Console.WriteLine("Caught exception");
    }
}

class TestModel : RealmObject
{
    public string Test { get; set; }

    public object ThisWillThrowBeforeConstruction = new ThrowingTest();

    internal class ThrowingTest
    {
        public ThrowingTest()
        {
            throw new Exception("die in ctor");
        }
    }
}

Stacktrace of the exception/crash you're getting

System.NullReferenceException: Object reference not set to an instance of an object.
   at Realms.RealmObjectBase.UnsubscribeFromNotifications()
   at Realms.RealmObjectBase.Finalize()

Relevant log output

No response