[3.7] Ensure zero byte files can be sent (#5125)

[aio-libs-github-bot]

Backports the following commits to 3.7:

• Ensure zero byte files can be sent (Ensure zero byte files can be sent #5125)

[codecov-io]

Codecov Report

Merging #5129 into 3.7 will decrease coverage by 0.90%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              3.7    #5129      +/-   ##
==========================================
- Coverage   97.11%   96.21%   -0.91%     
==========================================
  Files          44       44              
  Lines        8884     8875       -9     
  Branches     1426     1427       +1     
==========================================
- Hits         8628     8539      -89     
- Misses        131      199      +68     
- Partials      125      137      +12     

Flag	Coverage Δ
#unit	96.21% <100.00%> (-0.91%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
aiohttp/web_fileresponse.py	79.67% <100.00%> (-18.18%)	⬇️
aiohttp/http_websocket.py	95.21% <0.00%> (-3.47%)	⬇️
aiohttp/helpers.py	93.96% <0.00%> (-2.18%)	⬇️
aiohttp/frozenlist.py	95.83% <0.00%> (-2.09%)	⬇️
aiohttp/http_parser.py	95.48% <0.00%> (-2.04%)	⬇️
aiohttp/http_writer.py	97.24% <0.00%> (-1.84%)	⬇️
aiohttp/web_protocol.py	88.85% <0.00%> (-1.76%)	⬇️
aiohttp/web_response.py	97.83% <0.00%> (-0.44%)	⬇️
aiohttp/connector.py	94.49% <0.00%> (-0.32%)	⬇️
... and 8 more

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