[3.8] bpo-26407: Do not mask errors in csv. (GH-20536)

[serhiy-storchaka]

Unexpected errors in calling the iter method are no longer
masked by TypeError in csv.reader(), csv.writer.writerow() and
csv.writer.writerows().
(cherry picked from commit c88239f)

https://bugs.python.org/issue26407

[terryjreedy]

GHA tests do not give an error report. Travis says failure (unrelated) in test_nntplib

ERROR: test_descriptions (test.test_nntplib.NetworkedNNTP_SSLTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/build/python/cpython/Lib/test/test_nntplib.py", line 250, in wrapped
    meth(self)
  File "/home/travis/build/python/cpython/Lib/test/test_nntplib.py", line 99, in test_descriptions
    desc = descs[self.GROUP_NAME]
KeyError: 'comp.lang.python'
======================================================================
FAIL: test_description (test.test_nntplib.NetworkedNNTP_SSLTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/build/python/cpython/Lib/test/test_nntplib.py", line 250, in wrapped
    meth(self)
  File "/home/travis/build/python/cpython/Lib/test/test_nntplib.py", line 85, in test_description
    self.assertIn("Python", desc)
AssertionError: 'Python' not found in ''

Pipelines says more or less same including on Windows.  I will rerun in case transient.