Issue 460 - Optimization viewer fix for 0.0 bound values

[ScottDelbecq]

This PR resolves #460 by changing the manner to that bounds were not NaN in optimization viewer to avoid 0.0 to be interpreted as NaN.

[codecov[bot]]

Codecov Report

Merging #461 (53169f4) into master (9c4e426) will increase coverage by 0.04%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #461      +/-   ##
==========================================
+ Coverage   89.47%   89.51%   +0.04%     
==========================================
  Files          73       73              
  Lines        4437     4435       -2     
  Branches      714      714              
==========================================
  Hits         3970     3970              
+ Misses        338      337       -1     
+ Partials      129      128       -1     

Impacted Files	Coverage Δ
src/fastoad/gui/optimization_viewer.py	73.30% <100.00%> (+0.61%)	:arrow_up:

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