Avoid warning (and dismissal) of objects in input array when using mb_convert_encoding

[remyroussel]

Since commit e5ab4e3, we allow TransactionProcessor::audit $data['diff'] arrays to be handled by mb_convert_encoding (only string was before).
Problem is when an object is inside array (first level or deeper nested), mb_convert_encoding triggers a warning (and object is filtered out of result).

Linked to issue #220

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.43%. Comparing base (94e297d) to head (8900218).
Report is 16 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #223      +/-   ##
==========================================
- Coverage   97.15%   96.43%   -0.72%     
==========================================
  Files          42       42              
  Lines        1721     1712       -9     
==========================================
- Hits         1672     1651      -21     
- Misses         49       61      +12     

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[DamienHarper]

Thanks @remyroussel 👍🏽

[DamienHarper]

fixed in 3.1.0