[Checkins] [zopefoundation/Zope] b6fa2a: Prevent Error in isHTML() (#577)

[Michael Howitz]

  Branch: refs/heads/master
  Home:   https://github.com/zopefoundation/Zope
  Commit: b6fa2ab19e9e5944343cad23dc9bc8d20baafe75
      https://github.com/zopefoundation/Zope/commit/b6fa2ab19e9e5944343cad23dc9bc8d20baafe75
  Author: Michael Howitz <mh at gocept.com>
  Date:   2019-05-02 (Thu, 02 May 2019)

  Changed paths:
    M CHANGES.rst
    M src/ZPublisher/HTTPResponse.py
    M src/ZPublisher/tests/testHTTPResponse.py

  Log Message:
  -----------
  Prevent Error in isHTML() (#577)

* Prevent Error in isHTML()

If the parameter cannot be decoded none of the following checkes can lead to `True`.
The last one even breaks on Python 3 because it tries to find a `text` in a `bytes` object.

* Add change log entry and test.