Don't overwrite existing __init__.py files in Python generator

[connorworley]

No description provided.

[codecov]

Codecov Report

Merging #175 into master will increase coverage by 0.00%.
The diff coverage is 66.66%.

@@           Coverage Diff           @@
##           master     #175   +/-   ##
=======================================
  Coverage   50.79%   50.79%           
=======================================
  Files          37       37           
  Lines        8314     8315    +1     
  Branches     1768     1768           
=======================================
+ Hits         4223     4224    +1     
  Misses       3778     3778           
  Partials      313      313           

Flag	Coverage Δ
#unit	50.79% <66.66%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
stone/backends/python_types.py	33.21% <0.00%> (ø)
stone/backend.py	83.07% <100.00%> (+0.08%)	⬆️

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[rogebrd]

LGTM