Add 2 internal test points and fix PartitionPath web root (must be empty).
Fix WebPath to add '/' if web root.

That means this test-comment should be false:
https://github.com/asciidoctor/asciidoctor/blob/ab1e0b9c45e5138394b089dac205fb6d854e15e6/lib/asciidoctor/path_resolver.rb#L38-L39