Python3: TypeError: cannot use a string pattern on a bytes-like object

[Peter Suter]

RTF viewing does not work in Python 3:

Traceback (most recent call last):
  File "trac\mimeview\api.py", line 810, in render
    result = renderer.render(context, full_mimetype,
  File "BasicOfficePreview.py", line 45, in render
    return self._render_rtf(content)
  File "BasicOfficePreview.py", line 169, in _render_rtf
    for paragraph in parse_rtf(content.read())])
  File "BasicOfficePreview.py", line 125, in parse_rtf
    m = rtf_token_re.match(source, pos)
TypeError: cannot use a string pattern on a bytes-like object

[Peter Suter]

In 17661:

BasicOfficePreviewPlugin: Python 3 support.
(fix #13740)