docs-to-pdf runs forever with circular links

[MitchellMarx]

Converting https://python.langchain.com/ runs forever because https://python.langchain.com/docs/expression_language/cookbook/tools --next leads to a previous page. npx docs-to-pdf --initialDocURLs="https://python.langchain.com/" --contentSelector="article" --paginationSelector="a.pagination-nav__link.pagination-nav__link--next" --coverImage="https://upload.wikimedia.org/wikipedia/commons/3/3f/LangChain_logo.png" --coverTitle="LangChain"