Vader swallows Given lines

Hi,

please have a look at the following vader file:

```
Given asciidoc (ATX headings);
= ATX title

== ATX heading level 1

=== ATX heading level 2

==== ATX heading level 3

===== ATX heading level 4

====== ATX heading level 5

[[someanchor1]]
=== ATX heading level 2 with preceding anchor line

.some label
== ATX heading level 1 with preceding label line

Execute (print all ATX headings):
echom 'START'
for l in getline(1, '$')
echom l
endfor
echom 'END'

Given asciidoc (Setext headings);
Setext title
============

Setext heading level 1
----------------------

Setext heading level 2
~~~~~~~~~~~~~~~~~~~~~~

Setext heading level 3
^^^^^^^^^^^^^^^^^^^^^^

Setext heading level 4
++++++++++++++++++++++

[[someanchor1]]
Setext heading level 2 with preceding anchor line
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.some label
Setext heading level 1 with preceding label line
------------------------------------------------

Execute (print all Setext headings):
echom 'START'
for l in getline(1, '$')
echom l
endfor
echom 'END'
```

When running `:Vader` this is the output:

```
START
= ATX title
== ATX heading level 1
=== ATX heading level 2
==== ATX heading level 3
===== ATX heading level 4
====== ATX heading level 5
[[someanchor1]]
=== ATX heading level 2 with preceding anchor line
.some label
END
START
Setext title
============
END
```

Vader obviously swallows some lines. At first it seemed to me that it does this when it encounters a line that:

- starts with `=` and
- the line before it is not empty

But if I add

```

== foo

== bar
```

to the end of the "ATX headings" Given block then only the `== bar` line is swallowed.

The behaviour is the same when I use a semicolon instead of a colon after the `Given` line and use indentation.

What is wrong here? It seems that Vader just always chokes on asciidoc syntax.