Fix use-after-free in ArrayObject::unset() with destructor

[iluuu1994]

Fixes GH-16646

[iluuu1994]

There are also some more issues with ArrayObject::exchangeArray(). I'll look at those while I'm at it.

[nielsdos]

I didnt properly check when I wrote my comment that we could simply delay destructors, but indeed this seems to work too in this case.

[Girgias]

global and $GLOBALS do be the bane of my existence with all the whack bugs it can create.

But this looks reasonable

[iluuu1994]

Along with references, error handlers and destructors. ^^ Unfortunately, they are also kind of useful. 😄

[Girgias]

Very true :')