Fixed consecutive calls for write_eof on Response

[kammala]

What do these changes do?

Fix runtime exception while trying to return Response, which calls write_eof inside view.

Now we can create views which can do some post-processing logic for response(e.g. send some metrics, log some useful info, etc) without affecting response time.

Are there changes in behavior for the user?

No

Related issue number

No

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• Add a new entry to CHANGES.rst
  • Choose any open position to avoid merge conflicts with other PRs.
  • Add a link to the issue you are fixing (if any) using #issue_number format at the end of changelog message. Use Pull Request number if there are no issues for PR or PR covers the issue only partially.

[codecov-io]

Codecov Report

Merging #1939 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1939      +/-   ##
==========================================
+ Coverage   97.05%   97.05%   +<.01%     
==========================================
  Files          37       37              
  Lines        7612     7614       +2     
  Branches     1328     1329       +1     
==========================================
+ Hits         7388     7390       +2     
  Misses        101      101              
  Partials      123      123

Impacted Files	Coverage Δ
aiohttp/web_response.py	98.62% <100%> (ø)	⬆️

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[asvetlov]

The PR is good, but
Please add a record to CHANGES.txt
You also might mention yourself in CONTRIBUTORS.txt. It's not required but why not?

[fafhrd91]

@asvetlov ping

[asvetlov]

Thanks!

[lock]

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