OpenSystemsDevelopment / qpdf

Calculate all subsections before reading subsection entries.

Duplicates some warnings for the time being.

Rename to Xref_table::subsection.
Return results instead of using out parameters.
Take on responsibility for throwing exception and calculation of offset of
first subsection entry.

Also, remove redundant clearing of the xref tabl during QPDF destruction.

Do not remove object from xref table as this is only required when the
the method is called from within QPDF::Xref_table.

To be encapsulated later.

Also, when recovering trailer from xref streams, pick the last valid
trailer encountered rather than the first.

In FUTURE, treat uninitialized object handles as null

Fixes fuzz issue 71689.

Change the return type to a std::pair<bool, QPDFObjectHandle> in order to
allow a default constructed object handle (which is currently returned to
indicate failure) to become a valid object.

Fix handling of hybrid reference files in QPDF::read_xrefTable

Fix #1242

Fix QPDF::recoverStreamLength

Tidy QPDF_Stream

Replace some std::shared_ptr parameters with reference parameters

Ensure QPDF m->all_pages and invalid_page_found are reset if
getAllPagesInternal throws an exception.

Fixes fuzz case 71624.

1. Make class final
2. Pass og parameter by value
3. Properly initialize qpdf and og

Also, tweak QPDF::replaceObject to allow stream replacement without
violating the requirement that streams must always be indirect objects.

Also, remove QPDF::reserveStream as it does not do what the name implies
and having this as a separate methods does not aid code readability.

Given that the PDF spec requires the xref table to contain entries for all
object ids <= the maximum id present in a PDF document, max_size is a
qpdf implementation limitation for legitimate object ids.