Add missing to Encoding of Levtype iceLayerOnWater

[stefaniereuter]

Encoding issues in IceLayerOnWater fields. Missing was missing for some fields.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 22.91%. Comparing base (23ddfc3) to head (68596bb).
Report is 6 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/multio/action/encode/GribEncoder.cc	0.00%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #44      +/-   ##
===========================================
- Coverage    22.91%   22.91%   -0.01%     
===========================================
  Files          292      292              
  Lines        30582    30587       +5     
  Branches      1169     1170       +1     
===========================================
  Hits          7009     7009              
- Misses       23573    23578       +5     

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