Add check for positive float precision for non-shortest float_style

[quinnj]

Fixes #383

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.92%. Comparing base (cba1b4a) to head (55e2dff).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #393      +/-   ##
==========================================
+ Coverage   89.89%   89.92%   +0.03%     
==========================================
  Files           7        7              
  Lines        1316     1320       +4     
==========================================
+ Hits         1183     1187       +4     
  Misses        133      133              

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