Indentation issues in description lists with tagged regions

I think there is a bug in the indentations within [description lists](https://asciidoctor.org/docs/user-manual/#description-list). For example, while playing with the Glossary in https://github.com/elastic/stack-docs/pull/1214, I noticed this:


Notice that the description of the first item in the "L" description list (in this case, "leader index") is not indented. [I don't think this bug is specific to our build tools, since the same thing happens when I build via Asciidoctor directly (e.g. `asciidoctor stack-docs/docs/en/stack/index-landinall.adoc -r asciidoctor-diagram -a data-uri -D output/docs`)].

The specific scenario where this seems to happen is when you're including content from [tagged regions](https://asciidoctor.org/docs/user-manual/#by-tagged-regions) in the first item in the description list. Subsequent items have no such indentation issues. For example, here's an example of the source that hits this problem:

````
[[l-glos]] L::

[[glossary-leader-index]] leader index:::
+
--
include::{es-repo-dir}/glossary.asciidoc[tag=leader-index-def]
--

[[glossary-local-cluster]] local cluster:::
+
--
include::{es-repo-dir}/glossary.asciidoc[tag=local-cluster-def]
--
````

When you look at the output, you can see that the nesting of dl for the first item doesn't match the second item (i.e. it's nested incorrectly):

````