Broken links in breadcrumbs outside nav

When pages are not in the nav.adoc, the Antora UI creates broken links in the breadcrumbs and page titles.

To replicate the issue include the following files in any project:

```adoc
// modules/ROOT/nav.adoc
# ...
* xref:root-link.adoc[]
# ...
```

```adoc
// modules/ROOT/pages/root-link.adoc
= Root link

xref:test:A.adoc[A]

```

```adoc
// modules/test/pages/A.adoc
= A with a link to xref:B/B.adoc[B]

Link to xref:B/B.adoc[B]

```

```adoc
// modules/test/pages/B/B.adoc
= B with a link to xref:A.adoc[A]

Link to xref:A.adoc[A]

```

The links in B will be broken in the breadcrumbs and the title, but not in the content of the B.adoc file.