AttributeError in PDF export

[timobrembeck]

Describe the Bug

When a link has no link text, the PDF fails with an AttributeError.
This is the case when images are embedded with <img> tags.

Steps to Reproduce

1. Insert img tag in page
2. Export as PDF
3. See error

Expected Behavior

The PDF should be created

Actual Behavior

An error occurs:

AttributeError: 'NoneType' object has no attribute 'split'

Additional Information

Traceback

Apr 24 10:25:04 ERROR   django.request - 500 Internal Server Error: /lkmuenchen/de/wp-json/ig-mpdf/v1/pdf/?url=%2Flkmuenchen%2Fde%2Finformationen-fuer-menschen-aus-der-ukraine%2Faufenthaltserlaubnis-beantragen
Traceback (most recent call last):
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/core/handlers/exception.py", line 47, in inner
  response = get_response(request)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/core/handlers/base.py", line 181, in _get_response
  response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/integreat_cms/api/decorators.py", line 123, in wrap
  return function(request, *args, **kwargs)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/integreat_cms/api/v3/pdf_export.py", line 57, in pdf_export
  return generate_pdf(region, language_slug, pages)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/views/decorators/cache.py", line 44, in _wrapped_view_func
  response = view_func(request, *args, **kwargs)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/integreat_cms/cms/utils/pdf_utils.py", line 107, in generate_pdf
  html = get_template("pages/page_pdf.html").render(context)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/template/backends/django.py", line 61, in render
  return self.template.render(context)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/template/base.py", line 170, in render
  return self._render(context)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/template/base.py", line 162, in _render
  return self.nodelist.render(context)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/template/base.py", line 938, in render
  bit = node.render_annotated(context)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/template/base.py", line 905, in render_annotated
  return self.render(context)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/template/defaulttags.py", line 214, in render
  nodelist.append(node.render_annotated(context))
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/template/base.py", line 905, in render_annotated
  return self.render(context)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/template/base.py", line 988, in render
  output = self.filter_expression.resolve(context)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/template/base.py", line 698, in resolve
  new_obj = func(obj, *arg_vals)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/integreat_cms/cms/templatetags/pdf_filters.py", line 57, in pdf_truncate_links
  Truncator(word).chars(max_chars) for word in elem.text.split(" ")
AttributeError: 'NoneType' object has no attribute 'split'

This is a regression of #2164.