Web optimized PDFs improperly parsed

[ndvo]

When parsing a file that was web optimized the resulting root_object contains only :Size and :ID.

Steps to reproduce:

Select a PDF file and optimize it for the web:
- You can use this tool for it: https://tools.pdf24.org/en/optimize-pdf
- Upload the protected file and get the optimized file

   file = CombinePDF::PDFParser.new(value.read, allow_optional_content: true)
   file.parse
   file.root_object

Result will be something like:

{:Size=>6, :ID=>["\x00\x00\x00...\x00", "19v\x00\x00...\x00"]}