Bug: `samples/mkdocs-material`: Table of Contents indexes incorrectly when the PDF truncates.

[domWalters]

Related to #34

When #34 happens, the ToC has the page of all missing sections set to 0.

[dpinol]

What I realized is that these syntaxes work:

nav:
  - section1: section1.md
  - section2:
      - page1: page1.md

But this one doesn't:

nav:
  - section1:
      - page1.md