Fix rare invalid output in float to string conversion

[cschreib]

Fixes #193

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.16%. Comparing base (fe9249d) to head (57c90b4).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #194      +/-   ##
==========================================
- Coverage   94.17%   94.16%   -0.02%     
==========================================
  Files          30       30              
  Lines        1750     1747       -3     
==========================================
- Hits         1648     1645       -3     
  Misses        102      102              

Files with missing lines	Coverage Δ
include/snitch/snitch_append.hpp	96.07% <100.00%> (-0.08%)	⬇️

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