checking if reader is None

[khudyakovavi]

Getting errors when connection was closed:

  File "/usr/local/lib/python3.6/site-packages/tornado/gen.py", line 1069, in run
    yielded = self.gen.send(value)
  File "<string>", line 6, in _wrap_awaitable
  File "/usr/local/lib/python3.6/site-packages/cian_core/context/_stack_context.py", line 70, in wrapper
    val = yielded.send(res)
  File "/usr/local/lib/python3.6/site-packages/aioredis/connection.py", line 199, in _read_data
    if (obj == b'' or obj is None) and self._reader.at_eof():
AttributeError: 'NoneType' object has no attribute 'at_eof'

[webknjaz]

LGTM, but could you also add a test for that?

[codecov]

Codecov Report

Merging #447 into master will decrease coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #447      +/-   ##
=========================================
- Coverage   96.85%   96.8%   -0.06%     
=========================================
  Files          56      56              
  Lines        7831    7831              
  Branches      548     548              
=========================================
- Hits         7585    7581       -4     
- Misses        177     180       +3     
- Partials       69      70       +1

Impacted Files	Coverage Δ
aioredis/sentinel/pool.py	80.82% <0%> (-1.51%)	⬇️

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[seandstewart]

This change has been superseded by #891.