Fix #189 hstore when using ReadDictCursor

[angaz]

I saw the PR that hadn't been completed, so I made my own to get the fix merged. I hope it's what you are looking for.

I didn't know where to put the test. I hope I chose a good place.

[codecov]

Codecov Report

Merging #512 into master will increase coverage by 0.1%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master     #512     +/-   ##
=========================================
+ Coverage   93.66%   93.76%   +0.1%     
=========================================
  Files          25       25             
  Lines        3744     3756     +12     
  Branches      199      199             
=========================================
+ Hits         3507     3522     +15     
+ Misses        199      196      -3     
  Partials       38       38

Impacted Files	Coverage Δ
tests/test_connection.py	98.27% <100%> (+0.04%)	⬆️
tests/test_sa_types.py	90.42% <0%> (+3.19%)	⬆️

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