Don't close event loop if the loop doesn't exist

[asvetlov]

Fixes #257

[codecov-commenter]

Codecov Report

Merging #261 (953d9a1) into master (6cc430c) will increase coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #261      +/-   ##
==========================================
+ Coverage   92.98%   93.13%   +0.15%     
==========================================
  Files           3        3              
  Lines         228      233       +5     
  Branches       32       33       +1     
==========================================
+ Hits          212      217       +5     
  Misses         10       10              
  Partials        6        6              

Impacted Files	Coverage Δ
plugin.py	92.98% <0.00%> (+0.15%)	⬆️

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[asvetlov]

Ready for review, tests are green

[zanieb]

Thanks! This implementation lgtm