Bug(.landscape): mermaid diagram overlapping the next content

I found another bug with landscape mode and mermaid diagrams.
They are placed inside and all over the following content.

You can label this as low prio too. Normal orientation works fine and else I might just mention to look at a external file for now.

## I did
`quarkdown c --pdf bug.qd`

```quarkdown

.doctype {paged}
.theme {paperwhite} layout:{minimal}

## Heading 1
.landscape
.mermaid
.read {zeitplan.mmd}

## Heading 2
```

```
%% zeitplan.mmd
gantt
dateFormat HH:mm
axisFormat %H:%M

section ham
foo :20:30, 30m

section spam
bar :21:30, 30m

section eggs
bas :23:30, 30m
```

## What happens

Reproduce the issue with `quarkdown c --pdf bug.qd`, using the embedded `zeitplan.mmd` Mermaid chart and landscape block. Trace the PDF layout path for landscape Mermaid content and compare it with normal orientation. Done means the generated PDF keeps the Mermaid diagram within its page and does not overlap the following Heading 2 content.

Written by the indexing model from the issue text.