page-numbering-start-at and running-content-start-at keys with value 1 treated as 2

[mojavelinux]

There's an error in the min value computation of the body offset such that when either the page-numbering-start-at or running-content-start-at key is set to 1, it's treated as through it is set to 2. As a result, the first chapter in the following document is labeled as "ii" instead of 1.

= Document Title
:doctype: book

== Chapter Title

The behavior is correct if the value of the key is the symbolic name body.