GEOPY-2659: MVI: Add small value to reference amplitude if reference are used

[domfournier]

GEOPY-2659 - MVI: Add small value to reference amplitude if reference are used

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.06%. Comparing base (8a9f866) to head (8c7db56).
⚠️ Report is 4 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #337   +/-   ##
========================================
  Coverage    91.06%   91.06%           
========================================
  Files          117      117           
  Lines         6400     6403    +3     
  Branches       774      775    +1     
========================================
+ Hits          5828     5831    +3     
  Misses         380      380           
  Partials       192      192           

Files with missing lines	Coverage Δ
simpeg_drivers/components/models.py	91.15% <100.00%> (+0.07%)	⬆️

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