fix crash on expired node

[Doprez]

I noticed a crash when the player picks up the rifle then the pistol they can't pick up any of the physics cubes.

This just checks if the joint was expired before trying to change the attachment node. I also saw a couple typos that should now be fixed as well.

[gleblebedev]

@Doprez what do you think... Shall we do the same as Unity, i.e. when code checks for equality to null check if the node expired and return true if it is?

[Doprez]

I think that makes sense, I dont see the average user understanding why/when this could be a possibility.

If it isnt in an overridden equality check, then maybe an extension method that allows this in a single line check like IsValid or IsAlive. This would at least make the user think about the lifespan of a Node and it would be easy enough to document.

public static bool IsAlive(this RefCounted reference)
{
    return reference is not null && !reference.IsExpired;
}

Either would work in my eyes but one has the learning benefit.