Fix error handling bugs in _elementtree.c. (GH-10060)


References could leak, NULL could be dereferenced, and the Expat parser could
be double freed when some errors raised.
(cherry picked from commit 9f3ed3e213b30059087d059a7d1d3b2527fa8654)

Co-authored-by: Zackery Spytz <zspytz@gmail.com>
1 file changed