fixes #2092 nng_close may hang on Windows

[gdamore]

fixes #

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.01%. Comparing base (c4ca483) to head (dba356d).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2095      +/-   ##
==========================================
+ Coverage   83.98%   84.01%   +0.02%     
==========================================
  Files          93       93              
  Lines       23496    23496              
  Branches     3032     3032              
==========================================
+ Hits        19733    19739       +6     
+ Misses       3684     3682       -2     
+ Partials       79       75       -4     

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