OpenSystemsDevelopment / qpdf

As a rule, we should avoid conditional compilation is it always causes
code paths that are sometimes not even seen lexically by the compiler.
Also, we want the actual code being fuzzed to be as close as possible
to the real code. Conditional compilation is suitable to handle
underlying system differences.

Instead, favor configuration using callbacks or other methods that can
be triggered in the places where they need to be exercised.

Invalid entries are created when objects in the stream do not have
an existing xref entry.

Ensure objects with impossibly large ids are ignored.

Add extra fuzz test case and amend memory limit for Pl_DCT.

In QPDF::read_xrefEntry add buffer overflow test for first eol character.
Overlong f1 or f2 entries consisting only of zeros could cause a buffer
overflow.

Add fuzz testcase 69913.

Refine handling of severely damaged files

Also add new fuzz test case.

Refactor QPDF::parse_xrefEntry

QPDF::processXRefStream

Change the processed Index array to a vector of <first object, number of
entries> pairs.

Add closure damaged to create damagedPDF exceptions.

Tune processing of subsections.

Tune pointer arithmetic.

Apply temporary fix to deal with fuzz case 68915.

(Error is an integer overflow which would immediately cause a runtime error
as a result of a call to QInitCQIntC::to_size.)

Create set without creation of an intermediate vector.

Move reading of the entry from read_xrefTable to parse_xrefEntry.

Split parse_xrefEntry into two new methods read_xrefEntry and
read_bad_xrefEntry. read_xrefEntry is optimised for reading
correct entries. To handle incorrect entries it calls read_bad_xrefEntry,
which is largely unchanged from parse_xrefEntry.

Fix two errors introduced in #1110 and #1112. Since
#1110, encountering the invalid indirect reference #1110
-2147483648 n R produces an integer underflow which, if
 undetected, immediately trigger a logic error. Since
 #1112, object -1 0 R may be incorrectly identified as
 an earlier generation of itself and deleted,
 invalidating a live iterator.

Change set visited to std::vector<bool>

Swap front and back, and change queue from list to vector