HTML field attaches empty paragraphs

## Gentics Mesh Version
- v1.3.2

## Problem
When using WYSIWYG editor in HTML fields, empty p tags are attached before Headings & Lists

## Steps to reproduce

1. In CMS: Open node with HTML field
2. Add text including Headings & Lists
3. Save and Publish changes
4. Open the same node and/or the page rendering text from CMS

## Expected behaviour

Rendered HTML has the same structure as text in WYSIWYG Editor

## Actual behaviour

1. Additional whitespace is added in WYSIWYG Editor
2. Empty p tags are attached before Headings & Lists in rendered HTML:

```

Start by reproducing the issue in the CMS with an HTML field containing headings and lists, then inspect the WYSIWYG editor behavior and the saved rendered HTML. Done means the editor no longer adds extra whitespace and rendered HTML does not contain empty p elements before headings or lists.

Written by the indexing model from the issue text.