Backport stream header fix

[ahopkins]

This is a backport of #1957 to the last LTS.

See also #1730 and #1653.

[codecov]

Codecov Report

Merging #1959 into 19.12LTS will increase coverage by 0.56%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##           19.12LTS    #1959      +/-   ##
============================================
+ Coverage     89.38%   89.95%   +0.56%     
============================================
  Files            25       25              
  Lines          2930     2936       +6     
  Branches        543      544       +1     
============================================
+ Hits           2619     2641      +22     
+ Misses          237      222      -15     
+ Partials         74       73       -1     

Impacted Files	Coverage Δ
sanic/request.py	99.60% <ø> (ø)
sanic/router.py	95.49% <ø> (ø)
sanic/worker.py	84.29% <ø> (+1.65%)	⬆️
sanic/__version__.py	100.00% <100.00%> (ø)
sanic/asgi.py	94.08% <100.00%> (+3.27%)	⬆️
sanic/response.py	100.00% <100.00%> (ø)
sanic/server.py	75.28% <0.00%> (+1.79%)	⬆️

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[ashleysommer]

Go ahead and merge and release 19.12.3