Fix post op - pydeface

[arnaudbore]

This PR should fix this issue #258

[codecov-commenter]

Codecov Report

Patch coverage: 20.00% and project coverage change: -2.36% ⚠️

Comparison is base (cb4bdb8) 78.60% compared to head (89e3fbb) 76.25%.
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #260      +/-   ##
==========================================
- Coverage   78.60%   76.25%   -2.36%     
==========================================
  Files          15       15              
  Lines        1019     1057      +38     
  Branches      217      232      +15     
==========================================
+ Hits          801      806       +5     
- Misses        171      203      +32     
- Partials       47       48       +1     

Flag	Coverage Δ
pytest	76.25% <20.00%> (-2.36%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
dcm2bids/sidecar.py	81.01% <0.00%> (-0.52%)	⬇️
dcm2bids/acquisition.py	77.24% <6.89%> (-16.78%)	⬇️
dcm2bids/dcm2bids_gen.py	76.34% <50.00%> (-4.12%)	⬇️

... and 1 file with indirect coverage changes

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