According to an example in the PDF specification, see http://www.adobe.com/content/dam/Adobe/en/devnet/acrobat/pdfs/PDF32000_2008.pdf#page=56, an `ObjStm` stream should not contain 'endobj' commands. Fixes 5241. Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=898610. Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1037816.