misc/freebsd-doc-*: Update to rev. 719bd81 from the FreeBSD docset

• Update to rev. 719bd81 from the FreeBSD docset (1)
• Add a check for PDF build dependencies (2)

PR: 264109 (1), 262820 (2)
Reported by: Graham Perrin <grahamperrin@gmail.com> (1)

Alessandro Sagratini <ale_sagra@hotmail.com> (2)