* Fix stack overflow when partially-__init__ Node raises exception.
* If a Node subclass raises an exception and ctypes is in use before
__init_handle_by_constructor__ is called (or self.handle is
otherwise set), a Python stack overflow could result. This is
because the unset handle slot causes self.handle accesses to
fallback on the getattr(self, 'handle') method, invoking
NodeGetAttr.
* Then I believe this causes an infinite loop.
* The fix is to make Node.__getattr__ raise AttributeError for all
attributes in __slots__, then make __del__ tolerant to missing
self.handle.
* I don't believe cython is affected because it implements a
descriptor to access its underlying chandle and that shouldn't be unset.
* black format
* actually use handle instead of self.handle
Andrew Reusch
929717a03a