While the Outline Items making up the document's Outline have all sorts
of cross-references (parent, first/last chlid, next/previous sibling,
etc), not all documents out there have fully-consistent references. Our
implementation already discarded some of that information too (e.g.,
/Parent and /Prev were never read), and trusted that /First and /Next
were good enough to traverse the whole hierarchy.
Where the current implementation failed was in assuming that /Last was
also a good source of information. There are documents out there were
/Last also points to dead ends, and were therefore causing a crash when
we verified that the last child found on a chain was the /Last child
declared by the parent. To fix this I'm simply removing the check, and
simplifying the function call to remove any references to /Last. This
way we affirm our commitment to /First and /Next as the main sources of
information.
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