Prevent double closing when client connection is released before the last data_received() callback.

[asvetlov]

Fix #3031

[codecov-io]

Codecov Report

Merging #3079 into master will decrease coverage by 0.01%.
The diff coverage is 50%.

@@            Coverage Diff            @@
##           master   #3079      +/-   ##
=========================================
- Coverage   98.11%   98.1%   -0.02%     
=========================================
  Files          42      42              
  Lines        7750    7751       +1     
  Branches     1349    1350       +1     
=========================================
  Hits         7604    7604              
  Misses         51      51              
- Partials       95      96       +1

Impacted Files	Coverage Δ
aiohttp/client_proto.py	95.36% <50%> (-0.64%)	⬇️

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[new issue]: https://github.com/aio-libs/aiohttp/issues/new