A section naming an /XRefStm that a newer section had already read
skipped the stream entirely, so an entry in its own table that
disagreed with the stream was no longer recorded in xref_oddities.
Signature validation reads those records to refuse an appended section
another reader could follow. The reader keeps each hybrid stream's
entries (up to MAX_XREF_OBJECTS in all) and compares every later
naming section's table with them, without decoding the stream again.