Fix EOL detection at end of file without a trailing newline

[rpoelstra]

I've a PDF with a '%%EOF' comment that ends without a newline character. This caused a TypeError exception in comment() on line 187.
I've fixed this by including EOF (None) as a valid EOL marker.

If you accept this PR it would be great if you can make a new release also, so I can convert back to my normal workflow :)

[maxpmaxp]

@rpoelstra can you share the document with me please?

[rpoelstra]

Unfortunately, I can't share this document due to sensitive information inside the document. Redacting the document removes the tricky situation which pdfreader is unable to handle.

But in essence this PR also treats EOF as EOL, which seems logical as a line cannot extend beyond the end of the document.

[maxpmaxp]

@rpoelstra let me rephrase my question then. Does your file end with %%EOF or does it have some other trailing characters after %%EOF?

[rpoelstra]

The end of the file looks like this:

Note however, that there also exist PDF files without the '0a' at the end that parse fine, so it also seems to depend on the command structure inside the PDF.