`ClassMetadata.descriptor`'s `ptr` is sometimes `nil`

[NSExceptional]

Not sure what other information I need to provide, but just ask! I'm trying to inspect Swift classes in third party apps.

[NSExceptional]

In this instance it seems to be happening when you have a class defined in Swift, and then at runtime it is subclassed, and that subclass is what has the issue.

It's probably not an "issue" but it is something I'm not sure how to handle yet.

For context, this is something Firebase does to your app delegate

[NSExceptional]

I have updated my own fork with a fix; lmk if it's one you want to merge. I made SignedPointer have an implicitly unwrapped! pointer, and I made ClassMetadata.descriptor optional and forcefully unwrapped it in your tests. Might add a test for "artificial subclasses" if you do want this merged