core: fix two more uninitialized members

Found by Coverity when scanning the bundled pdfium-3004 in LibreOffice.

This fixes:

- CID 1400335:  Uninitialized members  (UNINIT_CTOR)
  CPDF_DataAvail::m_dwTrailerOffset
- CID 1400334:  Uninitialized members  (UNINIT_CTOR)
  CXML_Element::m_pParent

Change-Id: I42da9a704ad75adf39c510c6ef89eb7a97860ea1
Reviewed-on: https://pdfium-review.googlesource.com/2670
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/AUTHORS b/AUTHORS
index 17a0c60..6c2a295 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -27,6 +27,7 @@
 Lucas Nihlen <luken@chromium.org>
 Matt Giuca <mgiuca@chromium.org>
 Michael Doppler <m.doppler@gmail.com>
+Miklos Vajna <vmiklos@vmiklos.hu>
 Nico Weber <thakis@chromium.org>
 Peter Kasting <pkasting@chromium.org>
 Raymes Khoury <raymes@chromium.org>