FIX: Mapping of dense fields

[oesteban]

Resolves: #267.

[codecov]

Codecov Report

❌ Patch coverage is 94.11765% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.00%. Comparing base (5647caf) to head (664552b).

Files with missing lines	Patch %	Lines
nitransforms/resampling.py	80.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #268      +/-   ##
==========================================
- Coverage   95.09%   95.00%   -0.10%     
==========================================
  Files          16       16              
  Lines        1979     1982       +3     
  Branches      265      265              
==========================================
+ Hits         1882     1883       +1     
  Misses         77       77              
- Partials       20       22       +2     

Flag	Coverage Δ
unittests	94.97% <94.11%> (-0.10%)	⬇️

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[oesteban]

merged into #266.