traceback on inconsistent journal object type and content

[quozl]

When a journal object with MIME-type set to application/pdf actually contains text/plain, Read reports this log;

1536845187.043496 ERROR read-activity: Can not load document:
  ev-document-error-quark: File type plain text document (text/plain) is not supported (0)

Traceback (most recent call last):
  File "/usr/bin/sugar-activity", line 219, in <module>
    main()
  File "/usr/bin/sugar-activity", line 214, in main
    instance = create_activity_instance(activity_constructor, activity_handle)
  File "/usr/bin/sugar-activity", line 48, in create_activity_instance
    activity = constructor(handle)
  File "/home/ibiam/Activities/read-activity/readactivity.py", line 366, in __init__
    self.read_file(self._jobject.file_path)
  File "/home/ibiam/Activities/read-activity/readactivity.py", line 731, in read_file
    self._load_document('file://' + tempfile)
  File "/home/ibiam/Activities/read-activity/readactivity.py", line 1033, in _load_document
    self._update_toc()
  File "/home/ibiam/Activities/read-activity/readactivity.py", line 611, in _update_toc
    if self._view.update_toc(self):
  File "/home/ibiam/Activities/read-activity/evinceadapter.py", line 278, in update_toc
    if not doc.has_document_links():
AttributeError: 'NoneType' object has no attribute 'has_document_links'

Reported by @chimosky.

Workaround; delete the journal object, it is corrupt. If the journal object can be created by any activity, then that other activity should be fixed.