Bug/backorder status when track inventory false

[nspinazz89]

Description

This PR resolves #2817 which makes orders permanently backordered when splitting. It simply checks when the config option track inventory levels is false and coerces the value of inventory units to be on hand.

Another potential option would be to have inventory on hand levels set to infinity (in the code, not the db) when the config option is false.

Checklist:

• [x] I have followed Pull Request guidelines
• [x] I have added a detailed description into each commit message
• [x] I have updated Guides and README accordingly to this change (if needed)
• [x] I have added tests to cover this change (if needed)

[octave]

👍

[kennyadsl]

Checking if this is still a bug. Locally the provided specs are not failing to remove the change to the fulfillment changer class. Just pushed the spec only to see if we are still effected. If everything is green, we can close this without merging.

[codecov[bot]]

Codecov Report

Merging #3338 (de85741) into master (5525671) will increase coverage by 0.01%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3338      +/-   ##
==========================================
+ Coverage   86.70%   86.71%   +0.01%     
==========================================
  Files         578      578              
  Lines       14688    14700      +12     
==========================================
+ Hits        12735    12747      +12     
  Misses       1953     1953              

Impacted Files	Coverage Δ
.../app/controllers/spree/api/shipments_controller.rb	93.13% <ø> (ø)
core/app/models/spree/fulfilment_changer.rb	100.00% <100.00%> (ø)

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[kennyadsl]

I can reproduce the failing spec. Will push an update soon.

[kennyadsl]

I pushed an updated version with more unit specs and the implementation of this suggestion.