OpenSystemsDevelopment / qpdf

Ordinarily the trailer doesn't contain any strings, so this is usually
a non-issue, but if the trailer contains strings, linearizing and
encrypting with object streams would include encrypted strings in the
trailer, which would blow out the padding because encrypted strings
are longer than their cleartext counterparts.

It's detected in QPDFWriter instead of at parse time because I can't
figure out how to construct a test case in a reasonable time. This
commit moves the fuzz file into the regular test suite for a QTC
coverage case.

Use destructors to pop the pipeline stack, and ensure that code that
pops the stack is actually popping the intended thing.

When seeing to a position based on a value read from the input, we are
prone to integer overflow (fuzz issue 15442). Seek in two stages to
move the overflow check into the input source code.

Just because we know an indirect reference is null, doesn't mean we
shouldn't keep it indirect.

For some reason, qpdf from the beginning was replacing indirect
references to null with literal null in arrays even after removing the
old behavior of flattening scalar references. This seems like a bad
idea.

This message used to only appear for PDF >= 1.2. The invalid name is
valid for PDF 1.0 and 1.1. However, since QPDFWriter may write a newer
version, it's better to detect and warn in all cases. Therefore make
the warning more informative.

This change works around STL problems with Embarcadero C++ Builder
version 10.2, but std::vector is more common than std::list in qpdf,
and this is a relatively new API, so an API change is tolerable.

Thanks to Thorsten Schöning <6223655+ams-tschoening@users.noreply.github.com>
for the fix.

There were a few cases that could be caused by invalid input rather
than bugs in the code which were throwing logic_error instead of
runtime_error.

This also reverts the addition of a new checkLinearization that
distinguishes errors from warnings. There's no practical distinction
between what was considered an error and what was considered a
warning.

Thanks to github user zdenop for supplying some additional
error-handling code.