[bugfix] remove nan loss in manual optimization

[tchaton]

What does this PR do?

This PR fixes progress bar displaying NaN loss in manual_optimization.

Fixes #5123

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[Borda]

lgtm

[codecov]

Codecov Report

Merging #5121 (5bb7406) into master (b4d926b) will increase coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #5121   +/-   ##
======================================
  Coverage      93%     93%           
======================================
  Files         134     134           
  Lines        9905    9911    +6     
======================================
+ Hits         9204    9210    +6     
  Misses        701     701