wsgi: ignore ssl.SSLZeroReturnError at request finish()

[temoto]

I believe this is correct way to deal with zero-read error at request finish. But please correct if wrong @eventlet/developers . Maybe better option to log client shutdown events, but then they are often considered log noise.

fixes #739

[temoto]

To test this patch:

• pip install -U https://github.com/eventlet/eventlet/archive/739-ssl-eof.zip
• run https server using eventlet.wsgi
• trigger by closing client connections mid-protocol (as in not after successful response)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e06bff1) 53% compared to head (f493084) 53%.

Additional details and impacted files

@@          Coverage Diff          @@
##           master   #787   +/-   ##
=====================================
  Coverage      53%    53%           
=====================================
  Files          88     88           
  Lines        9869   9871    +2     
  Branches     1848   1849    +1     
=====================================
+ Hits         5325   5327    +2     
  Misses       4156   4156           
  Partials      388    388           

Flag	Coverage Δ
ipv6	22% <0%> (-1%)	⬇️
py310epolls	52% <0%> (+<1%)	⬆️
py310poll	52% <0%> (-1%)	⬇️
py310selects	52% <0%> (-1%)	⬇️
py311epolls	52% <0%> (-1%)	⬇️
py312epolls	50% <0%> (-1%)	⬇️
py37epolls	50% <0%> (+<1%)	⬆️
py38epolls	52% <50%> (-1%)	⬇️
py38openssl	50% <50%> (-1%)	⬇️
py38poll	52% <50%> (-1%)	⬇️
py38selects	51% <50%> (-1%)	⬇️
py39dnspython1	50% <50%> (-1%)	⬇️
py39epolls	52% <50%> (-1%)	⬇️
py39poll	52% <50%> (-1%)	⬇️
py39selects	51% <50%> (-1%)	⬇️

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