vcl PDF tokenizer: fix EOF position when \r is not followed by \n

vcl PDF tokenizer: fix EOF position when \r is not followed by \n

Otherwise this would break partial tokenize when we only read a trailer
in the middle of the file: m_aEOFs.back() is one byte larger than
rStream.Tell(), so we reader past the end of the trailer, resulting in a
tokenize failure.

What's special about the bugdoc:

- it has 2 xrefs, the first is incomplete, and refers to a second which
is later in the file
- the object length is as indirect object, triggering an xref lookup
- the first EOF is followed by a \r, but then not with a \n

This results in reading past the end of the first trailer and then
triggering a lookup failure.

FWIW, pdfium does the same in
<https://pdfium.googlesource.com/pdfium/+/59d107323f6727bbd5f8a4d0843081790638a1dd/core/fpdfapi/parser/cpdf_syntax_parser.cpp#446>,
we're on in sync with it.

Change-Id: Ia556a25e333b5e4f1418d92a98d74358862120e2
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/115466
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins